Method, device, and system for transmitting signals in unlicensed band

ABSTRACT

A method, device, and system for receiving a downlink signal is provided. The method includes: detecting a Channel State Information Reference Signal (CSI-RS) in a time unit #n on an unlicensed band cell; verifying whether the CSI-RS is used for Discovery RS (DRS) using an initialization value of a CSI-RS sequence of the CSI-RS; and performing a Radio Resource Management (RRM) measurement when the CSI-RS is used for the DRS. The CSI-RS is used for the DRS when an index of the time unit #n is not used for the initialization value of the CSI-RS sequence

TECHNICAL FIELD

The present invention relates to a wireless communication system.Specifically, the present invention relates to a method, device, andsystem for performing transmission or reception of a signal in anunlicensed band.

BACKGROUND ART

In recent years, with an explosive increase of mobile traffic due to thespread of smart devices, it has been difficult to cope with data usagewhich increases for providing a cellular communication service only by aconventional licensed frequency spectrum or LTE-licensed frequency band.

In such a situation, a scheme that uses an unlicensed (alternatively,unauthorized, non-licensed, or license unnecessary) frequency spectrumor LTE-Unlicensed frequency band (e.g., 2.4 GHz band, 5 GHz band, or thelike) for providing the cellular communication service has been devisedas a solution for a spectrum shortage problem.

However, unlike the licensed band in which a communication serviceprovider secures an exclusive frequency use right through a proceduresuch as auction, or the like, in the unlicensed band, multiplecommunication facilities can be used simultaneously without limit whenonly a predetermined level of adjacent band protection regulation isobserved. As a result, when the unlicensed band is used in the cellularcommunication service, it is difficult to guarantee communicationquality at a level provided in the licensed band and an interferenceproblem with a conventional wireless communication device (e.g.,wireless LAN device) using the unlicensed band may occur.

Therefore, a research into a coexistence scheme with the conventionalunlicensed band device and a scheme for efficiently sharing a radiochannel needs to be preferentially made in order to settle an LTEtechnology in the unlicensed band. That is, a robust coexistencemechanism (RCM) needs to be developed in order to prevent a device usingthe LTE technology in the unlicensed band from influencing theconventional unlicensed band device.

DISCLOSURE Technical Problem

The present invention has been made in an effort to provide a method forefficiently transmitting/receiving a signal in a wireless communicationsystem, in particular, a cellular wireless communication system and anapparatus therefor. Further, the present invention has been made in aneffort to provide a method for efficiently transmitting/receiving asignal in a specific frequency band (e.g., unlicensed band) and anapparatus therefor.

Technical objects desired to be achieved in the present invention arenot limited to the aforementioned objects, and other technical objectsnot described above will be apparently understood by those skilled inthe art from the following disclosure.

Technical Solution

According to an embodiment of the present invention, a method of a basestation to transmit a downlink signal in a cellular communication systemincludes: selecting Channel State Information Reference Signal (CSI-RS)configuration information for a downlink cell from a CSI-RSconfiguration information set; transmitting the selected CSI-RSconfiguration information to a user equipment; and transmitting CSI-RSto the user equipment in the downlink cell according to the selectedCSI-RS configuration information, wherein each CSI-RS configurationinformation represents Orthogonal Frequency Division Multiplexing (OFDM)symbols for CSI-RS in a subframe including OFDM symbols #0 to #13,wherein when the downlink cell operates in a licensed band, the CSI-RSconfiguration information set is a first CSI-RS configurationinformation set including one or more first CSI-RS configurationinformation related to OFDM symbols #5/#6, one or more second CSI-RSconfiguration information related to OFDM symbols #9/#10, and one ormore third CSI-RS configuration information related to OFDM symbols#12/#13, wherein when the downlink cell operates in an unlicensed band,the CSI-RS configuration information set is a second CSI-RSconfiguration information set, wherein the second CSI-RS configurationinformation set is part of the first CSI-RS configuration set and doesnot include the one or more third CSI-RS configuration information.

According to another embodiment of the present invention, a base stationused in a cellular wireless communication system includes: a wirelesscommunication module; and a processor, wherein the processor isconfigured to select Channel State Information Reference Signal (CSI-RS)configuration information for a downlink cell from a CSI-RSconfiguration information set, transmit the selected CSI-RSconfiguration information to a user equipment, and transmit CSI-RS tothe user equipment in the downlink cell according to the selected CSI-RSconfiguration information, wherein each CSI-RS configuration informationrepresents Orthogonal Frequency Division Multiplexing (OFDM) symbols forCSI-RS in a subframe including OFDM symbols #0 to #13, wherein when thedownlink cell operates in a licensed band, the CSI-RS configurationinformation set is a first CSI-RS configuration information setincluding one or more first CSI-RS configuration information related toOFDM symbols #5/#6, one or more second CSI-RS configuration informationrelated to OFDM symbols #9/#10, and one or more third CSI-RSconfiguration information related to OFDM symbols #12/#13, wherein whenthe downlink cell operates in an unlicensed band, the CSI-RSconfiguration information set is a second CSI-RS configurationinformation set, wherein the second CSI-RS configuration information setis part of the first CSI-RS configuration set and does not include theone or more third CSI-RS configuration information.

The second CSI-RS configuration information set may not include the oneor more first CSI-RS configuration information.

The first CSI-RS configuration information set may be a CSI-RSconfiguration {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19} and the second CSI-RS configuration information set may be aCSI-RS configuration {1, 2, 3, 6, 7, 8, 12, 13, 14, 15, 16, 17}.

The OFDM symbols for CSI-RS according to a CSI-RS configuration is givenby the following Table.

Number of CSI reference signals configured 1 or 2 4 8 CSI-RS OFDM symbolOFDM symbol OFDM symbol configuration index index index 0 5, 6 5, 6 5, 61  9, 10  9, 10  9, 10 2  9, 10  9, 10  9, 10 3  9, 10  9, 10  9, 10 412, 13 12, 13 12, 13 5 5, 6 5, 6 6  9, 10  9, 10 7  9, 10  9, 10 8  9,10  9, 10 9 12, 13 12, 13 10 5, 6 11 5, 6 12  9, 10 13  9, 10 14  9, 1015  9, 10 16  9, 10 17  9, 10 18 12, 13 19 12, 13

The cellular communication system may be a 3rd Generation PartnershipProject (3GPP) Long-term Evolution (LTE)-based communication system.

According to another embodiment of the present invention, a method of auser equipment to receive a downlink signal in a cellular communicationsystem, the method including: detecting a Channel State InformationReference Signal (CSI-RS) in a time unit #n on an unlicensed band cell;verifying whether the CSI-RS may be used for Discovery RS (DRS) using aninitialization value of a CSI-RS sequence of the CSI-RS; and performinga Radio Resource Management (RRM) measurement using the CSI-RS when theCSI-RS may be used for the DRS, wherein when an index of the time unit#n may be not used for the initialization value of the CSI-RS sequence,the CSI-RS may be used for the DRS.

According to another embodiment of the present invention, a userequipment used in a cellular wireless communication system, the userequipment comprising: a wireless communication module; and a processor,wherein the processor may be configured to detect a Channel StateInformation Reference Signal (CSI-RS) in a time unit #n on an unlicensedband cell, verify whether the CSI-RS may be used for Discovery RS (DRS)using an initialization value of a CSI-RS sequence of the CSI-RS andperform a Radio Resource Management (RRM) measurement using the CSI-RSwhen the CSI-RS may be used for the DRS, wherein when an index of thetime unit #n may be not used for the initialization value of the CSI-RSsequence, the CSI-RS may be used for the DRS.

The time unit #n may be a subframe #n or a slot #n.

The time unit #n may be not a subframe #0 or #5, and when a slot indexof the subframe #0 or #5 may be used for the initialization value of theCSI-RS sequence, the CSI-RS may be used for the DRS.

When the CSI-RS may be used for the DRS, the CSI-RS may be used for theCSI measurement and the Radio Resource Management (RRM) measurement.

The initialization value of the CSI-RS sequence may be given by thefollowing Equation.

c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(CSI)+1)+2·N _(ID) ^(CSI)+N _(CP)

Here, l represents an OFDM symbol index within a slot,

N_(ID) ^(CS:) represents a value configured by higher layers or aphysical cell identifier,

N_(CP) has 0 or 1 depending on a Cyclic Prefix (CP) type, and

n_(s) has an index of the time unit #n or has another predeterminedvalue according to the use of a CSI-RS.

OFDM symbols indexes according to a CSI-RS configuration for the CSI-RSmay be given by the following Table.

Number of CSI reference signals configured 1 or 2 4 8 CSI-RS OFDM symbolOFDM symbol OFDM symbol configuration index index index 0 5, 6 5, 6 5, 61  9, 10  9, 10  9, 10 2  9, 10  9, 10  9, 10 3  9, 10  9, 10  9, 10 412, 13 12, 13 12, 13 5 5, 6 5, 6 6  9, 10  9, 10 7  9, 10  9, 10 8  9,10  9, 10 9 12, 13 12, 13 10 5, 6 11 5, 6 12  9, 10 13  9, 10 14  9, 1015  9, 10 16  9, 10 17  9, 10 18 12, 13 19 12, 13

When the CSI-RS is used for the DRS, the CSI-RS configuration for theCSI-RS may be one of the CSI-RS configuration {1, 2, 3, 6, 7, 8, 12, 13,14, 15, 16, 17} in the Table.

The cellular communication system is a 3rd Generation PartnershipProject (3GPP) Long-term Evolution (LTE)-based communication system.

According to another embodiment of the present invention, a base stationused in a cellular wireless communication system, the base stationcomprising: a wireless communication module; and a processor, whereinthe processor is configured to transmit a Channel State InformationReference Signal (CSI-RS) to a user equipment using an initializationvalue of a CSI-RS sequence for the CSI-RS on an unlicensed band cell,wherein the initialization value of the CSI-RS sequence is not generatedaccording to an index of a time unit #n when the CSI-RS is used for theDRS, wherein the CSI-RS is used for performing a Radio ResourceManagement (RRM) measurement on the user equipment.

The time unit #n may be a subframe #n or a slot #n.

The time unit #n may be not a subframe #0 or #5, and when a slot indexof the subframe #0 or #5 may be used for the initialization value of theCSI-RS sequence, the CSI-RS may be used for the DRS.

When the CSI-RS may be used for the DRS, the CSI-RS may be used for theCSI measurement and the Radio Resource Management (RRM) measurement.

The initialization value of the CSI-RS sequence may be given by thefollowing Equation.

c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(CSI)+1)+2·N _(ID) ^(CSI)+N _(CP)

Here, l represents an OFDM symbol index within a slot,

N_(ID) ^(CS:) represents a value configured by higher layers or aphysical cell identifier,

N_(CP) has 0 or 1 depending on a Cyclic Prefix (CP) type, and

n_(s) has an index of the time unit #n or has another predeterminedvalue according to the use of a CSI-RS.

OFDM symbols indexes according to a CSI-RS configuration for the CSI-RSmay be given by the following Table.

Number of CSI reference signals configured 1 or 2 4 8 CSI-RS OFDM symbolOFDM symbol OFDM symbol configuration index index index 0 5, 6 5, 6 5, 61  9, 10  9, 10  9, 10 2  9, 10  9, 10  9, 10 3  9, 10  9, 10  9, 10 412, 13 12, 13 12, 13 5 5, 6 5, 6 6  9, 10  9, 10 7  9, 10  9, 10 8  9,10  9, 10 9 12, 13 12, 13 10 5, 6 11 5, 6 12  9, 10 13  9, 10 14  9, 1015  9, 10 16  9, 10 17  9, 10 18 12, 13 19 12, 13

Advantageous Effects

According to exemplary embodiments of the present invention, providedare a method for efficiently transmitting/receiving a signal in awireless communication system, in particular, a cellular wirelesscommunication system and an apparatus therefor. Further, provided are amethod for efficiently transmitting/receiving a signal in a specificfrequency band (e.g., unlicensed band) and an apparatus therefor.

Effects to be acquired in the present invention are not limited to theaforementioned effects, and other effects not described above will beapparently understood by those skilled in the art from the followingdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to help understand the present invention, the accompanyingdrawings which are included as a part of the Detailed Descriptionprovide embodiments of the present invention and describe the technicalmatters of the present invention together with the Detailed Description.

FIG. 1 illustrates physical channels used in a 3rd generationpartnership project (3GPP) system and a general signal transmittingmethod using the physical channels.

FIG. 2 illustrates one example of a radio frame structure used in awireless communication system.

FIG. 3 illustrates one example of a downlink (DL)/uplink (UL) slotstructure in the wireless communication system.

FIG. 4 illustrates a structure of a downlink subframe (SF).

FIG. 5 illustrates a structure of an uplink subframe.

FIG. 6 is a diagram for describing single carrier communication andmulti-carrier communication.

FIG. 7 illustrates an example in which a cross carrier schedulingtechnique is applied.

FIG. 8 illustrates Discovery Reference Signal (DRS) transmission.

FIGS. 9 to 11 illustrate the structure of a reference signal used asDRS.

FIG. 12 illustrates a Licensed Assisted Access (LAA) serviceenvironment.

FIG. 13 illustrates a deployment scenario of a user equipment and a basestation in an LAA service environment.

FIG. 14 illustrates a conventional communication scheme operating in anunlicensed band.

FIGS. 15 to 16 illustrate a Listen-Before-Talk (LBT) procedure for DLtransmission.

FIG. 17 illustrates DL transmission in unlicensed band.

FIG. 18 illustrates DRS transmission in unlicensed band.

FIG. 19 illustrates a parameter for LAA DRS transmission and a DRStransmission method based on LBT.

FIGS. 20 and 21 illustrate LAA DRS+PDSCH simultaneous transmission inDMTC.

FIG. 22 illustrates an existing Secondary Synchronization Signal (SSS).

FIG. 22 illustrates a CSI-RS Resource Element (RE) according to a CSI-RSconfiguration.

FIG. 23 illustrates a CSI-RS transmitting process according to anembodiment of the present invention.

FIG. 24 illustrates a CSI-RS receiving process according to anotherembodiment of the present invention.

FIG. 25 illustrates a configuration of a user equipment and a basestation according to an embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Terms used in the specification adopt general terms which are currentlywidely used as possible by considering functions in the presentinvention, but the terms may be changed depending on an intention ofthose skilled in the art, customs, and emergence of new technology.Further, in a specific case, there is a term arbitrarily selected by anapplicant and in this case, a meaning thereof will be described in acorresponding description part of the invention. Accordingly, it intendsto be revealed that a term used in the specification should be analyzedbased on not just a name of the term but a substantial meaning of theterm and contents throughout the specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “equal to or more than” or “equal to orless than” based on a specific threshold may be appropriatelysubstituted with “more than” or “less than”, respectively in someexemplary embodiments.

The following technology may be used in various wireless access systems,such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-FDMA(SC-FDMA), and the like. The CDMA may be implemented by a radiotechnology such as universal terrestrial radio access (UTRA) orCDMA2000. The TDMA may be implemented by a radio technology such asglobal system for mobile communications (GSM)/general packet radioservice (GPRS)/enhanced data rates for GSM evolution (EDGE). The OFDMAmay be implemented by a radio technology such as IEEE 802.11(Wi-Fi),IEEE 802.16(WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), and the like.The UTRA is a part of a universal mobile telecommunication system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of an evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA) and LTE-advanced (A) is an evolvedversion of the 3GPP LTE. 3GPP LTE/LTE-A is primarily described for cleardescription, but technical spirit of the present invention is notlimited thereto.

FIG. 1 illustrates physical channels used in a 3GPP system and a generalsignal transmitting method using the physical channels. A user equipmentreceives information from a base station through downlink (DL) and theuser equipment transmits information through uplink (UL) to the basestation. The information transmitted/received between the base stationand the user equipment includes data and various control information andvarious physical channels exist according to a type/purpose of theinformation transmitted/received between the base station and the userequipment.

When a power of the user equipment is turned on or the user equipmentnewly enters a cell, the user equipment performs an initial cell searchoperation including synchronization with the base station, and the like(S301). To this end, the user equipment receives a primarysynchronization channel (P-SCH) and a secondary synchronization channel(S-SCH) from the base station to synchronize with the base station andobtain information including a cell ID, and the like. Thereafter, theuser equipment receives a physical broadcast channel from the basestation to obtain intra-cell broadcast information. The user equipmentreceives a downlink reference signal (DL RS) in an initial cell searchstep to verify a downlink channel state.

The user equipment that completes initial cell search receives aphysical downlink control channel (PDCCH) and a physical downlink sharedchannel (PDSCH) depending on information loaded on the PDCCH to obtainmore detailed system information (S302).

When there is no radio resource for initially accessing the base stationor signal transmission, the user equipment may perform a random accessprocedure (RACH procedure) to the base station (S303 to S306). To thisend, the user equipment may transmit a preamble through a physicalrandom access channel (PRACH) (S303) and receive a response message tothe preamble through the PDCCH and the PDSCH corresponding thereto(S304). In the case of a contention based RACH, a contention resolutionprocedure may be additionally performed.

Thereafter, the user equipment may receive the PDCCH/PDSCH (S307) andtransmit a physical uplink shared channel (PUSCH)/physical uplinkcontrol channel (PUCCH) (S308) as a general procedure. The userequipment receives downlink control information (DCI) through the PDCCH.The DCI includes control information such as resource allocationinformation to the user equipment and a format varies depending on a usepurpose. The control information which the user equipment transmits tothe base station is designated as uplink control information (UCI). TheUCI includes an acknowledgement/negative acknowledgement (ACK/NACK), achannel quality indicator (CQI), a precoding matrix index (PMI), a rankindicator (RI), and the like. The UCI may be transmitted through thePUSCH and/or PUCCH.

FIG. 2 illustrates one example of a radio frame structure used in awireless communication system. FIG. 2A illustrates a frame structure forfrequency division duplex (FDD) and FIG. 2B illustrates a framestructure for time division duplex (TDD).

Referring to FIG. 2, a radio frame may have a length of 10 ms (307200Ts) and be constituted by 10 subframes (SFs). Ts represents a samplingtime and is expressed as Ts=1/(2048*15 kHz). Each subframe may have alength of 1 ms and be constituted by 2 slots. Each slot has a length of0.5 ms. A time for transmitting one subframe is defined as atransmission time interval (TTI). A time resource may be distinguishedby radio frame numbers/indexes, subframe numbers/indexes #0 to #9, andslot numbers/indexes #0 to #19.

The radio frame may be configured differently according to a duplexmode. In an FDD mode, downlink transmission and uplink transmission aredistinguished by a frequency and the radio frame includes only one of adownlink subframe and an uplink subframe with respect to a specificfrequency band. In a TDD mode, the downlink transmission and the uplinktransmission are distinguished by a time and the radio frame includesboth the downlink subframe and the uplink subframe with respect to aspecific frequency band. The TDD radio frame further includes specialsubframes for downlink and uplink switching. The special subframeincludes a Downlink Pilot Time Slot (DwPTS), a guard period (GP), and anUplink Pilot Time Slot (UpPTS).

FIG. 3 illustrates a structure of a downlink/uplink slot.

Referring to FIG. 3, the slot includes a plurality of orthogonalfrequency divisional multiplexing (OFDM) symbols in a time domain and aplurality of resource blocks (RBs) in a frequency domain The OFDM symbolalso means one symbol period. The OFDM symbol may be called an OFDMAsymbol, a single carrier frequency division multiple access (SC-FDMA)symbol, or the like according to a multi-access scheme. The number ofOFDM symbols included in one slot may be variously modified according tothe length of a cyclic prefix (CP). For example, in the case of a normalCP, one slot includes 7 OFDM symbols and in the case of an extended CP,one slot includes 6 OFDM symbols. The RB is defined as NDL/ULsymb (e.g.,7) continuous OFDM symbols in the time domain and NRBsc (e.g., 12)continuous subcarriers in the frequency domain. A resource constitutedby one OFDM symbol and one subcarrier is referred to as a resourceelement (RE) or a tone. One RB is constituted by NDL/ULsymb*NRBscresource elements.

The resource of the slot may be expressed as a resource grid constitutedby NDL/ULRB*NRBsc subcarriers and NDL/ULsymb OFDM symbols. Each RE inthe resource grid is uniquely defined by an index pair (k, 1) for eachslot. k represents an index given with 0 to NDL/ULRB*NRBsc-1 in thefrequency domain and 1 represents an index given with 0 to NDL/ULsymb-1in the time domain. Herein, NDLRB represents the number of resourceblocks (RBs) in the downlink slot and NULRB represents the number of RBsin the UL slot. NDLRB and NULRB depend on a DL transmission bandwidthand a UL transmission bandwidth, respectively. NDLsymb represents thenumber of symbols in the downlink slot and NULsymb represents the numberof symbols in the UL slot. NRBsc represents the number of subcarriersconstituting one RB. One resource grid is provided per antenna port.

FIG. 4 illustrates a structure of a downlink subframe.

Referring to FIG. 4, the subframe may be constituted by 14 OFDM symbols.First 1 to 3 (alternatively, 2 to 4) OFDM symbols are used as a controlregion and the remaining 13 to 11 (alternatively, 12 to 10) OFDM symbolsare used as a data region according to subframe setting. R1 to R4represent reference signals for antenna ports 0 to 3. Control channelsallocated to the control region include a physical control formatindicator channel (PCFICH), a physical hybrid-ARQ indicator channel(PHICH), a physical downlink control channel (PDCCH), and the like. Datachannels allocated to the data region include the PDSCH, and the like.When an enhanced PDCCH (EPDCCH) is set, the PDSCH and the EPDCCH aremultiplexed by frequency division multiplexing (FDM) in the data region.

The PDCCH as the physical downlink control channel is allocated to firstn OFDM symbols of the subframe. n as an integer of 1 (alternatively, 2)or more is indicated by the PCFICH. The PDCCH announces informationassociated with resource allocation of a paging channel (PCH) and adownlink-shared channel (DL-SCH) as transmission channels, an uplinkscheduling grant, HARQ information, and the like to each user equipmentor user equipment group. Data (that is, transport block) of the PCH andthe DL-SCH are transmitted through the PDSCH. Each of the base stationand the user equipment generally transmit and receive data through thePDSCH except for specific control information or specific service data.

Information indicating to which user equipment (one or a plurality ofuser equipment) the data of the PDSCH is transmitted, informationindicating how the user equipment receive and decode the PDSCH data, andthe like are transmitted while being included in the PDCCH/EPDCCH. Forexample, it is assumed that the PDCCH/EPDCCH is CRC-masked with a radionetwork temporary identity (RNTI) called “A”and information regardingdata transmitted by using a radio resource (e.g., frequency location)called “B” and a DCI format called “C”, that is, transmission formatinformation (e.g., transport block size, modulation scheme, codinginformation, and the like) is transmitted through a specific subframe.In this case, a user equipment in the cell monitors the PDCCH/EPDCCH byusing the RNTI information thereof and when one or more user equipmenthaving the “A” RNTI are provided, the user equipment receives thePDCCH/EPDCCH and receive the PDSCH indicated by “B” and “C” throughinformation on the received PDCCH/EPDCCH.

FIG. 5 illustrates a structure of an uplink subframe.

Referring to FIG. 5, the subframe may be divided into the control regionand the data region in the frequency domain. The PUCCH is allocated tothe control region and carries the UCI. The PUSCH is allocated to thedata region and carries user data.

The PUCCH may be used to transmit the following control information.

Scheduling Request (SR): Information used to request a UL-SCH resource.The SR is transmitted by using an on-off keying (OOK) scheme.

HARQ-ACK: Response to the PDCCH and/or response to a downlink datapacket (e.g., codeword) on the PDSCH. The codeword is an encoded formatof the transport block. The HARQ-ACK indicates whether the PDCCH orPDSCH is successfully received. The HARQ-ACK response includes apositive ACK (simply, ACK), a negative ACK (NACK), discontinuoustransmission (DTX), or the NACK/DTX. The DTX represents a case in whichthe user equipment misses the PDCCH (alternatively, semi-persistentscheduling (SPS) PDSCH) and the NACK/DTX means the NACK or DTX. TheHARQ-ACK is mixedly used with the HARQ-ACK/NACK and the ACK/NACK.

Channel State Information (CSI): Feed-back information regarding thedownlink channel Multiple input multiple output (MIMO) related feed-backinformation includes the RI and the PMI.

Table 1 shows the relationship between a PUCCH format and the UCI.

TABLE 1 PUCCH Format Uplink control information (UCI) Format 1Scheduling request (SR) (non-modulated waveform) Format 1a 1-bit HARQACK/NACK (SR existence/non-existence) Format 1b 2-bit HARQ ACK/NACK (SRexistence/non-existence) Format 2 CSI (20 coded bits) Format 2 CSI and 1or 2-bit HARQ ACK/NACK (20 bits) (corresponding to only extended CP)Format 2a CSI and 1-bit HARQ ACK/NACK (20 + 1 coded bits) Format 2b CSIand 2-bit HARQ ACK/NACK (20 + 2 coded bits) Format 3 (LTE-A) HARQACK/NACK + SR (48 coded bits)

Hereinafter, carrier aggregation will be described. The carrieraggregation means a method in which the wireless communication systemuses a plurality of frequency blocks as one large logical frequency bandin order to use a wider frequency band. When a whole system band isextended by the carrier aggregation, a frequency band used forcommunication with each user equipment is defined by a component carrier(CC) unit.

FIG. 6 is a diagram for describing single carrier communication andmulti-carrier communication. FIG. 6A illustrates a subframe structure ofa single carrier and FIG. 6B illustrates a subframe structure ofmulti-carriers which are carrier-aggregated.

Referring to FIG. 6A, in a single carrier system, the base station andthe user equipment perform data communication through one DL band andone UL band corresponding thereto. The DL/UL band is divided into aplurality of orthogonal subcarriers and each frequency band operates atone carrier frequency. In the FDD, the DL and UL bands operate atdifferent carrier frequencies, respectively and in the TDD, the DL andUL bands operate at the same carrier frequency. The carrier frequencymeans a center frequency of the frequency band.

Referring to FIG. 6B, the carrier aggregation is distinguished from anOFDM system that performs DL/UL communication in a base frequency banddivided into a plurality of subcarriers by using one carrier frequency,in that the carrier aggregation performs DL/UL communication by using aplurality of carrier frequencies. Referring to FIG. 6B, three 20 MHz CCsare gathered in each of the UL and the DL to support a bandwidth of 60MHz. The CCs may be adjacent to each other or non-adjacent to each otherin the frequency domain. For convenience, FIG. 6B illustrates a case inwhich a bandwidth of a UL CC and a bandwidth of a DL CC are the same aseach other and symmetric to each other, but the bandwidths of therespective CCs may be independently decided. Further, asymmetric carrieraggregation in which the number of UL CCs and the number of DL CCs aredifferent from each other is also available. The DL/UL CC(s) areindependently allocated/configured for each user equipment and the DL/ULCC(s) allocated/configured to the user equipment are designated asserving UL/DL CC(s) of the corresponding user equipment.

The base station may activate some or all of serving CCs of the userequipment or deactivate some CCs. When the base station allocates theCC(s) to the user equipment, if the CC allocation to the user equipmentis wholly reconfigured or if the user equipment does not hand over, atleast one specific CC among the CC(s) configured with respect to thecorresponding user equipment is not deactivated. A specific CC which isalways activated is referred to as a primary CC (PCC) and a CC which thebase station may arbitrarily activate/deactivate is referred to as asecondary CC (SCC). The PCC and the SCC may be distinguished based onthe control information. For example, specific control information maybe set to be transmitted/received only through a specific CC and thespecific CC may be referred to as the PCC and remaining CC(s) may bereferred to as SCC(s). The PUCCH is transmitted only on the PCC.

In 3 GPP, a concept of the cell is used in order to manage the radioresource. The cell is defined as a combination of the DL resource andthe UL resource, that is, a combination of the DL CC and the UL CC. Thecell may be configured by the DL resource only or the combination of theDL resource and the UL resource. When the carrier aggregation issupported, a linkage between the carrier frequency of the DL resource(alternatively, DL CC) and the carrier frequency of the UL resource(alternatively, UL CC) may be indicated by system information. Forexample, the combination of the DL resource and the UL resource may beindicated by a system information block type 2 (SIB2) linkage. Thecarrier frequency means a center frequency of each cell or CC. A cellcorresponding to the PCC is referred to as the primary cell (PCell) anda cell corresponding to the SCC is referred to as the secondary cell(SCell). A carrier corresponding to the PCell is a DL PCC in thedownlink and a carrier corresponding to the PCell is a UL PCC in theuplink. Similarly, a carrier corresponding to the SCell is a DL SCC inthe downlink and a carrier corresponding to the SCell is a UL SCC in theuplink. According to a user equipment capability, the serving cell(s)may be constituted by one PCell and 0 or more SCells. For a userequipment which is in an RRC_CONNECTED state, but does not have anyconfiguration for the carrier aggregation or does not support thecarrier aggregation, only one serving cell constituted by only the PCellis present.

FIG. 7 illustrates an example in which cross carrier scheduling isapplied. When the cross carrier scheduling is configured, a controlchannel transmitted through a first CC may schedule a data channeltransmitted through the first CC or a second CC by using a carrierindicator field (CIF). The CIF is included in the DCI. In other words, ascheduling cell is configured, and a DL grant/UL grant transmitted in aPDCCH area of the scheduling cell schedules the PDSCH/PUSCH of ascheduled cell. That is, a search space for a plurality of componentcarriers is present in the PDCCH area of the scheduling cell. The PCellmay be basically the scheduling cell and a specific SCell may bedesignated as the scheduling cell by an upper layer.

In FIG. 7, it is assumed that three DL CCs are aggregated. Herein, DLcomponent carrier #0 is assumed as the DL PCC (alternatively, PCell) andDL component carrier #1 and DL component carrier #2 are assumed as theDL SCC (alternatively, SCell). Further, it is assumed that the DL PCC isset as a PDCCH monitoring CC. When the CIF is disabled, the respectiveDL CCs may transmit only the PDCCH that schedules the PDSCH thereofwithout the CIF according to an LTE PDCCH rule (non-cross carrierscheduling or self-carrier scheduling). On the contrary, when the CIF isenabled by UE-specific (alternatively, UE-group-specific orcell-specific) upper layer signaling, a specific CC (e.g., DL PCC) maytransmit the PDCCH scheduling the PDSCH of DL CC A and the PDCCHscheduling the PDSCH of another CC by using the CIF (cross-carrierscheduling). On the contrary, in another DL CC, the PDCCH is nottransmitted.

Hereinafter, DRS transmission in a licensed band will be described withreference to FIGS. 8 to 11. FIG. 8 illustrates DRS transmission, andFIGS. 9 to 11 illustrate a structure of a reference signal used in DRS.For convenience, DRS in the licensed band is referred to as Rel-12 DRS.DRS supports small cell on/off, and a SCell that is not active for anyuser equipment may be turned off except for DRS periodic transmission.Also, based on the DRS, a user equipment may obtain cell identificationinformation, measure Radio Resource Management (RRM), and obtaindownlink synchronization.

Referring to FIG. 8, a Discovery Measurement Timing Configuration (DMTC)indicates a time window in which a user equipment expects to receiveDRS. The DMTC is fixed at 6 ms. The DMTC period is the transmissionperiod of the DMTC, and may be 40 ms, 80 ms, or 160 ms. The position ofthe DMTC is specified by the DMTC transmission period and the DMTCoffset (in units of subframes), and these information are transmitted tothe user equipment through higher layer signaling (e.g., RRC signaling).DRS transmissions occur at the DRS occasion within the DMTC. The DRSoccasion has a transmission period of 40 ms, 80 ms or 160 ms, and theuser equipment may assume that there is one DRS occasion per DMTCperiod. The DRS occasion includes 1 to 5 consecutive subframes in theFDD radio frame and 2 to 5 consecutive subframes in the TDD radio frame.The length of the DRS occasion is delivered to the user equipment viahigher layer signaling (e.g., RRC signaling). The user equipment mayassume DRS in the DL subframe in the DRS occasion. DRS occasion mayexist anywhere in the DMTC, but the user equipment expects thetransmission interval of DRS s transmitted from the cell to be fixed(i.e., 40 ms, 80 ms, or 160 ms). That is, the position of the DRSoccasion in the DMTC is fixed per cell. The DRS is configured asfollows.

Cell-specific Reference Signal (CRS) at antenna port 0 (see FIG. 9): Itexists in all downlink subframes within the DRS occasion, and in theDwPTS of all the special subframes. The CRS is transmitted in the entireband of the subframe.

Primary Synchronization Signal (PSS) (see FIG. 10): In the case of FDDradio frame, it exists in the first subframe in DRS occasion, or in thesecond subframe in DRS occasion in the case of TDD radio frame. The PSSis transmitted in the seventh (or sixth) OFMDA symbol of the subframeand mapped to six RBs (=72 subcarriers) close to the center frequency.

Secondary Synchronization Signal (SSS) (see FIG. 10): It exists in thefirst subframe in the DRS occasion. The SSS is transmitted in the sixth(or fifth) OFMDA symbol of the subframe and mapped to six RBs (=72subcarriers) close to the center frequency.

non-zero-power Channel State Information (CSI)-RS (see FIG. 11): Itexists in zero or more subframes in the DRS occasion. The position ofthe non-zero-power CSI-RS is variously configured according to thenumber of CSI-RS ports and the higher layer configuration information.

FIG. 8 illustrates a case where the DRS reception time is set to aseparate DMTC for each frequency in a user equipment's situation.Referring to FIG. 8, in the case of frequency F1, a DRS occasion with alength of 2 ms is transmitted every 40 ms, in the case of frequency F2,a DRS occasion with a length of 3 ms is transmitted every 80 ms, and inthe case of frequency F3, a DRS occasion with a length of 4 ms istransmitted every 80 ms. The user equipment may know the startingposition of the DRS occasion in the DMTC from the subframe including theSSS. Here, the frequencies F1 to F3 may be replaced with correspondingcells, respectively.

Embodiment: DRS Transmission Scheme in Unlicensed Band

FIG. 12 illustrates a Licensed Assisted Access (LAA) serviceenvironment.

Referring to FIG. 12, a service environment may be provided to a user,in the service environment, an LTE technology (11) in a conventionallicensed band and LTE-unlicensed (LTE-U) or LAA which is an LTEtechnology (12) in an unlicensed band, which has been actively discussedmay be connected to each other. For example, the LTE technology (11) inthe licensed band and the LTE technology (12) in the unlicensed band inthe LAA environment may be integrated by using a technology such ascarrier aggregation, or the like, which may contribute to extension of anetwork capacity. Further, in an asymmetric traffic structure in whichthe amount of downlink data is more than that of uplink data, the LAAmay provide an optimized LTE service according to various requirementsor environments. For convenience, the LTE technology in the licensed(alternatively, authorized or permitted) band is referred to asLTE-licensed (LTE-L) and the LTE technology in the unlicensed(alternatively, unauthorized, non-licensed, license-unnecessary) band isreferred to as LTE-unlicensed (LTE-U) or LAA.

FIG. 13 illustrates a layout scenario of a user equipment and a basestation in an LAA service environment. A frequency band targeted by theLAA service environment has a short wireless communication reachdistance due to a high-frequency characteristic. By considering this,the layout scenario of the user equipment and the base station in anenvironment in which the conventional LTE-L service and the LAA servicecoexist may be an overlay model and a co-located model.

In the overlay model, a macro base station may perform wirelesscommunication with an X UE and an X′ UE in a macro area (32) by using alicensed carrier and be connected with multiple radio remote heads(RRHs) through an X2 interface. Each RRH may perform wirelesscommunication with an X UE or an X′ UE in a predetermined area (31) byusing an unlicensed carrier. The frequency bands of the macro basestation and the RRH are different from each other not to interfere witheach other, but data needs to be rapidly exchanged between the macrobase station and the RRH through the X2 interface in order to use theLAA service as an auxiliary downlink channel of the LTE-L servicethrough the carrier aggregation.

In the co-located model, a pico/femto base station may perform thewireless communication with a Y UE by using both the licensed carrierand the unlicensed carrier. However, it may be limited that thepico/femto base station uses both the LTE-L service and the LAA serviceto downlink transmission. A coverage (33) of the LTE-L service and acoverage (34) of the LAA service may be different according to thefrequency band, transmission power, and the like.

When LTE communication is performed in the unlicensed band, conventionalequipment (e.g., wireless LAN (Wi-Fi) equipment) which performcommunication in the corresponding unlicensed band may not demodulate anLTE-U message or data and determine the LTE-U message or data as a kindof energy to perform an interference avoidance operation by an energydetection technique. That is, when energy corresponding to the LTE-Umessage or data is lower than −62 dBm or certain energy detection (ED)threshold value, the wireless LAN equipment may perform communication bydisregarding the corresponding message or data. As a result, that userequipment which performs the LTE communication in the unlicensed bandmay be frequently interfered by the wireless LAN equipment.

Therefore, a specific frequency band needs to be allocated or reservedfor a specific time in order to effectively implement an LTE-Utechnology/service. However, since peripheral equipment which performcommunication through the unlicensed band attempt access based on theenergy detection technique, there is a problem in that an efficientLTE-U service is difficult. Therefore, a research into a coexistencescheme with the conventional unlicensed band device and a scheme forefficiently sharing a radio channel needs to be preferentially made inorder to settle the LTE-U technology. That is, a robust coexistencemechanism in which the LTE-U device does not influence the conventionalunlicensed band device needs to be developed.

FIG. 14 illustrates a communication scheme (e.g., wireless LAN) thatoperates in an unlicensed band in the related art. Since most devicesthat operate in the unlicensed band operate based on listen-before-talk(LBT), a clear channel assessment (CCA) technique that senses a channelbefore data transmission is performed.

Referring to FIG. 14, a wireless LAN device (e.g., AP or STA) checkswhether the channel is busy by performing carrier sensing beforetransmitting data. When a predetermined strength or more of radio signalis sensed in a channel to transmit data, it is determined that thecorresponding channel is busy and the wireless LAN device delays theaccess to the corresponding channel Such a process is referred to asclear channel evaluation and a signal level to decide whether the signalis sensed is referred to as a CCA threshold. Meanwhile, when the radiosignal is not sensed in the corresponding channel or a radio signalhaving a strength smaller than the CCA threshold is sensed, it isdetermined that the channel is idle.

When it is determined that the channel is idle, a terminal having datato be transmitted performs a back-off procedure after a defer period(e.g., arbitration interframe space (AIFS), PCF IFS (PIFS), or thelike). The defer period means a minimum time when the terminal needs towait after the channel is idle. The back-off procedure allows theterminal to further wait for a predetermined time after the deferperiod. For example, the terminal stands by while decreasing a slot timefor slot times corresponding to a random number allocated to theterminal in the contention window (CW) during the channel is in an idlestate, and a terminal that completely exhausts the slot time may attemptto access the corresponding channel.

When the terminal successfully accesses the channel, the terminal maytransmit data through the channel. When the data is successfullytransmitted, a CW size (CWS) is reset to an initial value (CWmin). Onthe contrary, when the data is unsuccessfully transmitted, the CWSincreases twice. As a result, the terminal is allocated with a newrandom number within a range which is twice larger than a previousrandom number range to perform the back-off procedure in a next CW. Inthe wireless LAN, only an ACK is defined as receiving responseinformation to the data transmission. Therefore, when the ACK isreceived with respect to the data transmission, the CWS is reset to theinitial value and when feed-back information is not received withrespect to the data transmission, the CWS increases twice.

As described above, since most communications in the unlicensed band inthe related art operate based on the LBT, the LTE also considers the LBTin the LAA for coexistence with the conventional device. In detail, inthe LTE, the channel access method on the unlicensed band may be dividedinto 4 following categories according to the presence/an applicationscheme of the LBT.

Category 1: No LBT

An LBT procedure by a Tx entity is not performed.

Category 2: LBT without random back-off

A time interval in which the channel needs to be sensed in an idle statebefore the Tx entity performs a transmission on the channel is decided.The random back-off is not performed.

Category 3: LBT with random back-off with a CW of fixed size

LBT method that performs random back-off by using a CW of a fixed size.The Tx entity has a random number N in the CW and the CW size is definedby a minimum/maximum value of N. The CW size is fixed. The random numberN is used to decide the time interval in which the channel needs to besensed in an idle state before the Tx entity performs a transmission onthe channel

Category 4: LBT with random back-off with a CW of variable size

LBT method that performs the random back-off by using a CW of a variablesize. The Tx entity has the random number N in the CW and the CW size isdefined by the minimum/maximum value of N. The Tx entity may change theCW size at the time of generating the random number N. The random numberN is used to decide the time interval in which the channel needs to besensed in an idle state before the Tx entity performs a transmission onthe channel

FIGS. 15 and 16 illustrate a DL transmitting process based on thecategory 4 LBT. The category 4 LBT may be used to guarantee fair channelaccess with Wi-Fi. Referring to FIGS. 15 and 16, the LBT processincludes initial CCA (ICCA) and extended CCA (ECCA). In the ICCA, therandom back-off is not performed and in the ECCA, the random back-off isperformed by using the CW of the variable size. The ICCA is applied tothe case in which the channel is idle when signal transmission isrequired and the ECCA is applied to the case in which the channel isbusy when the signal transmission is required or DL transmission isperformed just before. That is, it is determined whether the channel isidle through the ICCA, and data transmission is performed after the ICCAperiod. If the interference signal is detected and data transmissionfails, a data transmission time point may be obtained through a deferperiod +backoff counter after setting a random backoff counter.

Referring to FIG. 15, a signal transmitting process may be performed asfollows.

Initial CCA

S1202: The base station verifies that the channel is idle.

S1204: The base station verifies whether the signal transmission isrequired. When the signal transmission is not required, the processreturns to S1202 and when the signal transmission is required, theprocess proceeds to S1206.

S1206: The base station verifies whether the channel is idle for an ICCAdefer period (BCCA). The ICCA defer period is configurable. As animplementation example, the ICCA defer period may be constituted by aninterval of 16 μs and n consecutive CCA slots. Herein, n may be apositive integer and one CCA slot interval may be 9 μs. The number ofCCA slots may be configured differently according to a QoS class. TheICCA defer period may be set to an appropriate value by considering adefer period (e.g., DIFS or AlFS) of Wi-Fi. For example, the ICCA deferperiod may be 34 us. When the channel is idle for the ICCA defer period,the base station may perform the signal transmitting process (S1208).When it is determined that the channel is busy during the ICCA deferperiod, the process proceeds to S1212 (ECCA).

S1208: The base station may perform the signal transmitting process.When the signal transmission is not performed, the process proceeds toS1202 (ICCA) and when the signal transmission is performed, the processproceeds to S1210. Even in the case where a back-off counter N reaches 0in S1218 and S1208 is performed, when the signal transmission is notperformed, the process proceeds to S1202 (ICCA) and when the signaltransmission is performed, the process proceeds to S1210.

S1210: When additional signal transmission is not required, the processproceeds to S1202 (ICCA) and when the additional signal transmission isrequired, the process proceeds to S1212 (ECCA).

Extended CCA

S1212: The base station generates the random number N in the CW. N isused as a counter during the back-off process and generated from [0,q-1]. The CW may be constituted by q ECCA slots and an ECCA slot sizemay be 9 μs or 10 μs. The CW size (CWS) may be defined as q and bevariable in S1214. Thereafter, the base station proceeds to S1216.

S1214: The base station may update the CWS. The CWS q may be updated toa value between X and Y. The X and Y values are configurable parameters.CWS update/adjustment may be performed whenever N is generated (dynamicback-off) and semi-statically performed at a predetermined time interval(semi-static back-off). The CWS may be updated/adjusted based onexponential back-off or binary back-off. That is, the CWS may beupdated/adjusted in the form of the square of 2 or the multiple of 2. Inassociation with PDSCH transmission, the CWS may be updated/adjustedbased on feed-back/report (e.g., HARQ ACK/NACK) of the user equipment orupdated/adjusted based on base station sensing.

S1216: The base station verifies whether the channel is idle for an ECCAdefer period (DeCCA). The ECCA defer period is configurable. As animplementation example, the ECCA defer period may be constituted by aninterval of 16 μs and n consecutive CCA slots. Herein, n may be apositive integer and one CCA slot interval may be 9 μs. The number ofCCA slots may be configured differently according to the QoS class. TheECCA defer period may be set to the appropriate value by considering thedefer period (e.g., DIFS or AIFS) of Wi-Fi. For example, the ECCA deferperiod may be 34 us. When the channel is idle for the ECCA defer period,the base station proceeds to S1218. When it is determined that thechannel is busy during the ECCA defer period, the base station repeatsS1216.

S1218: The base station verifies whether N is 0. When N is 0, the basestation may perform the signal transmitting process (S1208). In thiscase, (N=0), the base station may not immediately perform transmissionand performs CCA check for at least one slot to continue the ECCAprocess. When N is not 0 (that is, N>0), the process proceeds to S1220.

S1220: The base station senses the channel during one ECCA slot interval(T). The ECCA slot size may be 9 μs or 10 μs and an actual sensing timemay be at least 4 μs.

S1222: When it is determined that the channel is idle, the processproceeds to S1224. When it is determined that the channel is busy, theprocess returns to S1216. That is, one ECCA defer period is appliedagain after the channel is idle and N is not counted during the ECCAdefer period.

S1224: N is decreased by 1 (ECCA countdown).

FIG. 16 is substantially the same as/similar to the transmitting processof FIG. 15 and is different from FIG. 15 according to an implementationscheme. Therefore, detailed matters may be described with reference tocontents of FIG. 15.

S1302: The base station verifies whether the signal transmission isrequired. When the signal transmission is not required, S1302 isrepeated and when the signal transmission is required, the processproceeds to S1304.

S1304: The base station verifies whether the slot is idle. When the slotis idle, the process proceeds to S1306 and when the slot is busy, theprocess proceeds to S1312 (ECCA). The slot may correspond to the CCAslot in FIG. 15.

S1306: The base station verifies whether the channel is idle for a deferperiod (D). D may correspond to the ICCA defer period in FIG. 15. Whenthe channel is idle for the defer period, the base station may performthe signal transmitting process (S1308). When it is determined that thechannel is busy during the defer period, the process proceeds to S1304.

S1308: The base station may perform the signal transmitting process ifnecessary.

S1310: When the signal transmission is not performed, the processproceeds to S1302 (ICCA) and when the signal transmission is performed,the process proceeds to S1312 (ECCA). Even in the case where theback-off counter N reaches 0 in S1318 and S1308 is performed, when thesignal transmission is not performed, the process proceeds to S1302(ICCA) and when the signal transmission is performed, the processproceeds to S1312 (ECCA).

Extended CCA

S1312: The base station generates the random number N in the CW. N isused as the counter during the back-off process and generated from [0,q-1]. The CW size (CWS) may be defined as q and be variable in S1314.Thereafter, the base station proceeds to S1316.

S1314: The base station may update the CWS. The CWS q may be updated tothe value between X and Y. The X and Y values are configurableparameters. CWS update/adjustment may be performed whenever N isgenerated (dynamic back-off) and semi-statically performed at apredetermined time interval (semi-static back-off). The CWS may beupdated/adjusted based on exponential back-off or binary back-off. Thatis, the CWS may be updated/adjusted in the form of the square of 2 orthe multiple of 2. In association with PDSCH transmission, the CWS maybe updated/adjusted based on feed-back/report (e.g., HARQ ACK/NACK) ofthe user equipment or updated/adjusted based on base station sensing.

S1316: The base station verifies whether the channel is idle for thedefer period (D). D may correspond to the ECCA defer period in FIG. 15.D in S1306 and D in S1316 may be the same as each other. When thechannel is idle for the defer period, the base station proceeds toS1318. When it is determined that the channel is busy during the deferperiod, the base station repeats S1316.

S1318: The base station verifies whether N is 0. When N is 0, the basestation may perform the signal transmitting process (S1308). In thiscase, (N=0), the base station may not immediately perform transmissionand performs CCA check during at least one slot to continue the ECCAprocess. When N is not 0 (that is, N>0), the process proceeds to S1320.

S1320: The base station selects one of an operation of decreasing N by 1(ECCA count-down) and an operation of not decreasing N (self-defer). Theself-defer operation may be performed according toimplementation/selection of the base station and the base station doesnot perform sensing for energy detection and not perform even ECCAcountdown in the self-defer.

S1322: The base station may select one of the operation not performingsensing for energy detection and the energy detecting operation. Whenthe sensing for the energy detection is not performed, the processproceeds to S1324. When the energy detecting operation is performed, ifan energy level is equal to or lower than an energy detection threshold(that is, idle), the process proceeds to S1324. If the energy level ishigher than the energy detection threshold (that is, busy), the processreturns to S1316. That is, one defer period is applied again after thechannel is idle and N is not counted during the defer period.

S1324: The process proceeds to S1318.

FIG. 17 illustrates an example in which a base station performs DLtransmission in an unlicensed band. The base station may aggregate cells(for convenience, LTE-L cell) of one or more licensed bands and cells(for convenience, LTE-U cell) of one or more unlicensed bands. In FIG.17, a case in which one LTE-L cell and one LTE-U cell are aggregated forcommunication with the user equipment is assumed. The LTE-L cell may bethe PCell and the LTE-U cell may be the SCell. In the LTE-L cell, thebase station may exclusively use the frequency resource and perform anoperation depending on LTE in the related art. Therefore, all of theradio frames may be constituted by regular subframes (rSF) having alength of 1 ms (see FIG. 2) and the DL transmission (e.g., PDCCH andPDSCH) may be performed every subframe (see FIG. 1). Meanwhile, in theLTE-U cell, the DL transmission is performed based on the LBT forcoexistence with the conventional device (e.g., Wi-Fi device). Further,a specific frequency band needs to be allocated or reserved for aspecific time in order to effectively implement the LTE-Utechnology/service. Therefore, in the LTE-U cell, the DL transmissionmay be performed through a set of one or more consecutive subframes (DLtransmission burst) after the LBT. The DL transmission burst may startas the regular subframe (rSF) or a partial subframe (pSF) according toan LBT situation. pSF may be a part of the subframe and may include asecond slot of the subframe. Further, the DL transmission burst may endas rSF or pSF.

Hereinafter, DRS transmission in an unlicensed band will be described.Using Rel-12 DRS on carriers within the unlicensed band introduces newlimitations. LBT regulation in some areas treats DRS as a short controltransmission, allowing DRS transmission without LBT. However, in someareas (such as Japan), LBT is also required for short controltransmissions. Therefore, it is required to apply the LBT to the DRStransmission on the LAA SCELL.

FIG. 18 illustrates DRS transmission in an unlicensed band. When LBT isapplied to DRS transmission, DRS may not be periodically transmitted dueto LBT failure in the unlicensed band, unlike Rel-12 DRS transmitted inthe licensed band. If the DRS transmission fails within the DMTC, thefollowing two options may be considered.

Alt1: The DRS may only be transmitted at a fixed time point within theDMTC. Therefore, when the DRS transmission fails, there is no DRStransmission in the DMTC.

Alt2: The DRS may be transmitted in at least one other time point withinthe DMTC. Thus, when a DRS transmission fails, a DRS transmission may beattempted at another time point within the DMTC.

Hereinafter, DRS transmission in an unlicensed band will be described.Specifically, a parameter for DRS transmission suitable for LAA based onDRS of 3GPP LTE Rel-12, a DRS transmission method, and the like aresuggested. For convenience, DRS in the existing licensed band isreferred to as Rel-12 DRS or LTE-L DRS, and DRS in the unlicensed bandis referred to as LAA DRS or LTE-U DRS.

FIG. 19 illustrates a parameter for LAA DRS transmission and a DRStransmission method based on LBT. The DRS transmission period isconfigured by the DMTC, and the DMTC period in the Rel-12 DRS isconfigured to 40/80/160 ms (see FIG. 8). However, when the channel ofthe transmission time point is busy due to the peripheral interferenceor the like in the case of the DRS transmitted in the LAA based on theLBT, the DRS may not be transmitted according to the DRS transmissionperiod. Therefore, if the DMTC period is configured to the same as thatin the LAA DRS, the transmission frequency of the LAA DRS may belowered. Therefore, a new DMTC period is required in the LAA, and may beconfigured to 40 ms or less, for example. In addition, the base stationmay attempt to transmit DRS at least once within the DMTC period, andmay configure a duration such as the DMTC and may be configured totransmit DRS in the corresponding duration. Accordingly, since the userequipment expects DRS transmission only in the DMTC, DRSsearch/detection is performed only in the corresponding DMTC, therebyreducing the power consumption of the user equipment and the burden ofblind detection/decoding. When a DRS transmission occurs in the DMTC,the base station transmits a DRS configuration (e.g., a configurationwith CRS/PSS/SSS/CSI-RS in Rel-12) when the channel is idle after LBT.DRS transmission duration may be defined as DRS occasion duration. TheDRS occasion duration in Rel-12 may be configured to 1 to 5 ms. SinceLAA operates based on LBT, as the DRS length (=DRS occasion duration)becomes longer, the transmittable time point decreases, and in the caseof long DRS, continuous transmission is required so that idle durationdoes not occur in order to prevent the transmission of other basestations/terminals/Wi-Fi devices based on LBT. FIG. 19 shows a DRSoccasion duration having a length of at least one subframe forconvenience, but the length of the DRS occasion duration is not limitedthereto. A method of transmitting DRS after LBT is broadly classifiedinto two. There are an Alt1 (DRS Alt. 1) technique, which allowstransmission from a fixed location (for convenience, the DMTC startinglocation) in the DMTC based on the LBT, and an Alt2 (DRS Alt. 2)technique, which allows at least one other DRS transmission even if theCCA result channel is busy in the DMTC and the DRS transmission fails.

FIG. 20 illustrates a case where simultaneous transmission of LAADRS+PDSCH occurs in SF #0/#5 in the LAA DMTC, and FIG. 21 illustrates acase where simultaneous transmission of LAA DRS+PDSCH occurs in SFexcept for SF #0/#5 in LAA DMTC. SF #0/#5 represents SF #0 and/or SF #5.In the LAA DRS transmission, the last two OFDM symbols of the SF (e. g.,OFDM symbol index #12/#13) are used as the CCA interval for the LBT ofthe next transmission. Therefore, the last two OFDM symbols of SF arenot used for LAA DRS transmission.

As shown in FIG. 21, when the DRS transmission is moved to the SF otherthan the SF #0/#5 due to the LBT, the PSS/SSS/CRS/CSI-RS that configuresthe DRS is transmitted in the OFDM symbol index within the correspondingSF which is same as the OFDM symbol index within the SF #0/#5. That is,the PSS (DRS) configuring the DRS is transmitted in the last OFDM symbol(e.g., symbol index #6) of the first slot in the corresponding SF, andthe SSS configuring the DRS is transmitted in the OFDM symbol index #5ahead of the PSS in the corresponding SF. Also, the CSI-RS configuringthe DRS is transmitted in the OFDM symbol index #9/#10.

In this case (i.e., DRS is transmitted in the SF except SF #0/#5),CSI-RS configured for periodic or aperiodic CSI-RS/CSI-InterferenceMeasurement (IM) and DRS collide with each other, so that CSI-RS/CSI-IMmeasurements (briefly, CSI measurements) may be affected. That is, whenCSI-RS is configured in an OFDM symbol index where DRS (e.g., PSS/SSS)is transmitted, the CSI-RS/CSI-IM measurement may not be performed, orthe measurement performance may deteriorate. Accordingly, there may be aproblem in ensuring reliability in the CSI-RS/CSI-IM measurement.

Hereinafter, in an embodiment of the present invention, a method forenabling CSI-RS/CSI-IM measurement when DRS transmission is performedand ensuring the accuracy and reliability of CSI-RS/CSI-IM measurementwill be described. An embodiment of the present invention may be appliedwhen DRS is transmitted on a cell in an unlicensed band (e.g., LAASCell). An embodiment of the present invention may be limited to a casewhere DRS is transmitted in SF other than SF #0/#5 (due to LBT etc.).Further, an embodiment of the present invention may be performed on theassumption that the base station explicitly or implicitly indicates thesignaling for the DRS transmission to the user equipment. Forconvenience of explanation, (DRS) is added to the signal configuring theDRS. That is, the PSS/SSS/CRS/CSI-RS configuring the DRS may beexpressed as PSS/SSS/CRS/CSI-RS (DRS). In addition, the CSI-RSconfiguring the DRS is denoted by CSI-RS (DRS), and the configuration ofthe CSI-RS configuring the DRS may be denoted by the CSI-RS (DRS)configuration. Meanwhile, the CSI-RS for CSI-RS/CSI-IM may be simplyrepresented as CSI-RS/CSI-IM or may be represented as CSI-RS(CSI-RS/CSI-IM). The configuration of the CSI-RS for CSI-RS/CSI-IM maybe expressed in a CSI-RS/CSI-IM configuration or in a CSI-RSconfiguration.

First, the conventional CSI-RS configuration will be described. FIG. 22illustrates the location of REs (CRI-RS RE) occupied by the CSI-RS inthe SF according to the number of antennas or the number of CSI-RS portsin one cell. Specifically, the resource mapping according to the CSI-RSconfiguration is determined by Table 2. Table 2 corresponds to Table 6.10.5.2-1 of 3GPP TS 36.211 V12.6.0. FIG. 22 and Table 2 correspond tothe case of the normal CP. The CSI reference signal configuration istransmitted via RRC signaling. Specifically, the CSI reference signalconfiguration is specified by the resourceConfig of theMeasCSI-RS-Config which is an RRC parameter.

TABLE 2 CSI reference Number of CSI reference signals configured signal1 or 2 4 8 configuration (k′, l′) n_(s) mod 2 (k′, l′) n_(s) mod 2 (k′,l′) n_(s) mod 2 Frame structure 0 (9, 5) 0 (9, 5) 0 (9, 5) 0 type 1 and2 1 (11, 2) 1 (11, 2) 1 (11, 2) 1 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 3 (7, 2)1 (7, 2) 1 (7, 2) 1 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8, 5) 0 6(10, 2) 1 (10, 2) 1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5) 1(8, 5) 1 10 (3, 5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 1 15(2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame structure20 (11, 1) 1 (11, 1) 1 (11, 1) 1 21 (9, 1) 1 (9, 1) 1 (9, 1) 1 22 (7, 1)1 (7, 1) 1 (7, 1) 1 23 (10, 1) 1 (10, 1) 1 24 (8, 1) 1 (8, 1) 1 25(6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 1 28 (3, 1) 1 29 (2, 1) 1 30(1, 1) 1 31 (0, 1) 1

Here, k′ is used to specify the subcarrier position, and l′ is used tospecify the OFDM symbol index within the slot. n_(s) represents a slotindex (0 to 19) in a radio frame (see FIG. 2). mod represents a modulooperation.

Specifically, the CSI-RS is transmitted periodically through 1, 2, 4 or8 antenna ports (e.g., p=15, p=15 to 16, p=15 to 18, p=15 to 22) and theRS sequence r_(l,n) _(s) (m) in the subframe configured for the CSI-RStransmission is mapped to the complex-valued modulation symbol a_(k,l)^((p)) as shown in Equation 1. a_(k,l) ^((p)) is used as a referencesymbol on the antenna port p.

                                     [Equation   1]  a_(k, l)^((p)) = w_(l^(″)) ⋅ r_(l, n_(s))(m^(′)),   where$\mspace{20mu} {k = {k^{\prime} + {12m} + \{ {{\begin{matrix}{{- 0}\ } & {{{{for}\mspace{14mu} p} \in \{ {{15},{16}} \}},\ {{normal}\mspace{20mu} {cyclic}\ {prefix}}} \\{{- 6}\ } & {{{{for}\mspace{14mu} p} \in \{ {17,18} \}},\ {{normal}\mspace{20mu} {cyclic}\ {prefix}}} \\{{- 1}\mspace{9mu}} & {{{{for}\mspace{14mu} p} \in \{ {19,{20}} \}},{{normal}\mspace{20mu} {cyclic}\ {prefix}}} \\{- 7} & {{{{for}\mspace{14mu} p} \in \{ {21,{22}} \}},{{normal}\mspace{20mu} {cyclic}\ {prefix}}} \\{{- 0}\;} & {{{{for}\mspace{14mu} p} \in \{ {15,{16}} \}},{{extended}\mspace{14mu} {cyclic}\ {prefix}}} \\{{- 3}\ } & {{{{for}\mspace{14mu} p} \in \{ {17,{18}} \}},{{extended}\mspace{14mu} {cyclic}\ {prefix}}} \\{{- 6}\;} & {{{{for}\mspace{14mu} p} \in \{ {19,{20}} \}},{{extended}\mspace{14mu} {cyclic}\ {prefix}}} \\{- 9} & {{{{for}\mspace{14mu} p} \in \{ {21,{22}} \}},{{extended}\mspace{14mu} {cyclic}\ {prefix}}}\end{matrix}l} = {l^{\prime} + \{ {{\begin{matrix}l^{''} & {{{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{20mu} {configurations}\mspace{20mu} 0{­19}},{{normal}\mspace{20mu} {cyclic}\ {prefix}}}\ } \\{2l^{''}} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{20mu} {configurations}\mspace{14mu} 20{­31}},\ {{normal}\mspace{20mu} {cyclic}\ {prefix}}} \\l^{''} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{20mu} {configurations}\mspace{14mu} 0­\ 27},\ {{extended}\mspace{14mu} {cyclic}\ {prefix}}}\end{matrix}\mspace{20mu} w_{l^{\prime}}} = \{ {{{\begin{matrix}1 & {p \in \{ {{15},{17},{19},{21}} \}} \\( {- 1} )^{l^{''}} & {p \in \{ {{16},{18},{20},{22}} \}}\end{matrix}\mspace{20mu} l^{''}} = 0},{{1\mspace{20mu} m} = 0},1,\ldots \mspace{14mu},{{N_{RB}^{DL} - {1\mspace{20mu} m^{\prime}}} = {m + \lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \rfloor}}} } }} }}$

Here, k represents a subcarrier index (refer to FIG. 3), and lrepresents an OFDM symbol index within the slot (refer to FIG. 3).N_(RB) ^(DL) represents the number of RBs in the DL band, and N_(RB)^(maxDL) represents the number of RBs in the maximum DL band.

Referring to Table 2 and Equation 1, the CSI-RS configuration (orresourceConfig) allocated to the OFDM symbol indexes #5 and #6 in thefirst slot is {0, 5, 10, 11} and the CSI-RS configuration allocated tothe OFDM symbol indexes #5 and #6 in the second slot or the OFDM symbolindexes #12 and #13 in the SF is {4, 9, 18, 19}. In addition, the CSI-RSconfiguration allocated to the OFDM symbol indexes #9 and #10 in the SFis {1, 2, 3, 6, 7, 8, 12, 13, 14, 15, 16, 17}.

Case 1) if CSI-RS is configured in DRS in unlicensed band cell

When CSI-RS is configured in DRS, the configuration of CSI-RS thatconfigures DRS is CSI-RS configuration using OFDM symbol index #9/#10(SF reference). Therefore, the CSI-RS configuration within the DMTC inthe unlicensed band cell may be set to only the CSI-RS configurationallocated to the OFDM symbol #9/#10. Meanwhile, CSI-RS (DRS) and CSI-RS(CSI-RS/CSI-IM) are configured independently. Also, even if the DRStransmission is moved to the SF other than the SF #0/#5 due to the LBT,in order to enable CSI-RS/CSI-IM measurements, the base station may setthe CSI-RS/CSI-IM configuration, MeasCSI-RS-Config which is the RRCparameter, to one of resourceConfig {1, 2, 3, 6, 7, 8, 12, 13, 14, 15,16, 17} except for resourceConfig {0, 4, 5, 9, 10, 11, 18, 19} or one ina subset of resourceConfig {1, 2, 3, 6, 7, 8, 12, 13, 14, 15, 16, 17},like the CSI-RS (DRS) configuration. A value of the CSI-RS configurationrefers to Table 2. By configuring the CSI-RS/CSI-IM configuration assame as the CSI-RS (DRS) configuration, the collision of CSI-RS(CSI-RS/CSI-IM) and PSS/SSS (DRS) may be prevented and CSI measurementmay be performed even when simultaneous transmission of PDSCH and DRS isperformed. Thus, when the user equipment is configured to performCSI-RS/CSI-IM measurements, the user equipment may assume thatresourceConfig {0, 4, 5, 9, 10, 11, 18, 19} is not used for theCSI-RS/CSI-IM measurements. That is, when the user equipment isconfigured to perform CSI-RS/CSI-IM measurements, in the expectationthat the CSI-RS/CSI-IM configuration is set to one of resourceConfig {1,2, 3, 6, 7, 8, 12, 13, 14, 15, 16, 17} or one of a subset ofresourceConfig {1, 2, 3, 6, 7, 8, 12, 13, 14, 15, 16, 17}, the userequipment may perform the CSI-RS/CSI-IM measurements.

To summarize, for an unlicensed band cell (e.g., LAA cell, LAA SCell),the base station may set a CSI-RS configuration to one of {1, 2, 3, 6,7, 8, 12, 13, 14, 15, 16, 17} or to only {1, 2, 3, 6, 7, 8, 12, 13, 14,15, 16, 17}. The user equipment may assume that a CSI-RS configurationof the unlicensed band cell may be set to one of {1, 2, 3, 6, 7, 8, 12,13, 14, 15, 16, 17} or one of a subset of {1, 2, 3, 6, 7, 8, 12, 13, 14,15, 16, 17}. That is, the base station may exclude the CSI-RSconfiguration {0, 4, 5, 9, 10, 11, 18, 19} in the unlicensed band cell,and the user equipment may assume that CSI-RS configuration {0, 4, 5, 9,10, 11, 18, 19} is not used in the unlicensed band cell. On the otherhand, there is no restriction on the CSI-RS configuration of licensedband cell. That is, the base station may use the CSI-RS configuration ofTable 2 without limitation to configure the CSI-RS of the licensed bandcell. That is, for the licensed band cell, the base station may set theCSI-RS configuration to one of {1, 2, . . . , 19}. The user equipmentmay assume that the CSI-RS configuration of the licensed band cell isset to one of {1, 2, . . . , 19}.

Also, an embodiment of the present invention may include a case where aresource (e.g., RE) mapped to CSI-RS (CSI-RS/CSI-IM) and a resourcemapped to CSI-RS(DRS) are the same, in addition to a case where a CSI-RS(DRS) configuration and a CSI-RS/CSI-IM configuration are the same. Inaddition, the number of antenna ports of the CSI-RS (DRS) and the numberof antenna ports of the CSI-RS (CSI-RS/CSI-IM) may be configured to bedifferent from each other. In this case, if CSI-RS configurations areset to be equal to each other, REs to which CSI-RS (DRS) andCSI-RS/CSI-IM are mapped in time and frequency resources may overlapeach other. At this time, the user equipment performs CSI measurementand/or RRM measurement based on the assumption of CSI-RS (DRS)transmission from the base station or performs CSI measurement based onthe assumption of CSI-RS (CSI-RS/CSI-IM) transmission from the basestation.

FIG. 23 illustrates a downlink transmitting process according to anembodiment of the present invention. The cellular communication systemto which an embodiment of the present invention is applied may belimited to a 3GPP LTE-based communication system.

Referring to FIG. 23, the base station may select CSI-RS configurationinformation for the downlink cell from the CSI-RS configurationinformation set (S2302). The CSI-RS configuration information mayindicate OFDM symbols for CSI-RS in a subframe including OFDM symbols #0to #13 (see Table 2). Then, the base station may transmit the selectedCSI-RS configuration information to the user equipment (S2304).Thereafter, the base station may transmit the CSI-RS to the userequipment in the downlink cell according to the selected CSI-RSconfiguration information (S2306). Here, the range of the CSI-RSconfiguration information set may vary according to thecharacteristics/classes/types of the band in which the downlink celloperates.

Specifically, when the downlink cell operates in the licensed band, theCSI-RS configuration information set may be a first CSI-RS configurationinformation set including one or more first CSI-RS configurationinformation related to the OFDM symbols #5/#6, one or more second CSI-RSconfiguration information related to the OFDM symbols #9/#10, and one ormore third CSI-RS configuration information related to the OFDM symbols#12/#13. On the other hand, when the downlink cell operates in theunlicensed band, the CSI-RS configuration information set is a secondCSI-RS configuration information set, and the second CSI-RSconfiguration information set may be part of the first CSI-RSconfiguration information set and not include the one or more thirdCSI-RS configuration information. Also, the second CSI-RS configurationinformation set may not include one or more first CSI-RS configurationinformation.

More specifically, the first CSI-RS configuration information set may bea CSI-RS configuration {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,14, 15, 16, 17, 18, 19} and the second CSI-RS configuration informationset may be a CSI-RS configuration {1, 2, 3, 6, 7, 8, 12, 13, 14, 15, 16,17}.

In this case, the OFDM symbols for CSI-RS according to a CSI-RSconfiguration may be given by the following table. More details mayrefer to Table 2.

Number of CSI reference signals configured 1 or 2 4 8 CSI-RS OFDM symbolOFDM symbol OFDM symbol configuration index index index 0 5, 6 5, 6 5, 61  9, 10  9, 10  9, 10 2  9, 10  9, 10  9, 10 3  9, 10  9, 10  9, 10 412, 13 12, 13 12, 13 5 5, 6 5, 6 6  9, 10  9, 10 7  9, 10  9, 10 8  9,10  9, 10 9 12, 13 12, 13 10 5, 6 11 5, 6 12  9, 10 13  9, 10 14  9, 1015  9, 10 16  9, 10 17  9, 10 18 12, 13 19 12, 13

As another example, even if the DRS transmission is moved to the SFother than the SF #0/#5 due to LBT, in order to enable CSI-RS/CSI-IMmeasurements, the CSI-RS configuration that may be allocated to the OFDMsymbol indexes #5 and #6 to which the PSS/SSS (DRS) is allocated may beexcluded when configuring the CSI-RS for an unlicensed band cell. Thatis, the CSI-RS for the unlicensed band cell may be configured using onlythe CSI-RS configuration not allocated to the OFDM symbol indexes #5 and#6. Specifically, in the unlicensed band cell, the CSI-RS configurationmay be set to one of resourceConfig {1, 2, 3, 4, 6, 7, 8, 9, 12, 13, 14,15, 16, 17, 18, 19} except resourceConfig{0, 5, 10, 11} or one of asubset of resourceConfig {1, 2, 3, 4, 6, 7, 8, 9, 12, 13, 14, 15, 16,17, 18, 19}. A value of the CSI-RS configuration refers to Table 2. Inthe case of DRS alone transmission, the last two OFDM symbols of an SFare used as the CCA interval for LBT of next transmission, but when DRSand PDSCH are multiplexed in the SF except the SF #0/#5, the last twoOFDM symbols of the SF may be used for PDSCH transmission and CSI-RS.Therefore, by configuring the CSI-RS configuration excluding the CSI-RSconfiguration, which may collide with the PSS/SSS (DRS), to anunlicensed band cell (e.g., LAA SCell), CSI-RS/CSI-IM measurement may beperformed even when DRS and PDSCH are multiplexed. When the userequipment is configured to perform CSI-RS/CSI-IM measurements, the userequipment may assume that resourceConfig {0, 5, 10, 11} is not used forthe CSI-RS/CSI-IM measurements. Thus, the user equipment may expect thatthe CSI-RS/CSI-IM configuration is set to one of resourceConfig {1, 2,3, 4, 6, 7, 8, 9, 12, 13, 14, 15, 16, 17, 18, 19} or one of a subset ofresourceConfig {1, 2, 3, 4, 6, 7, 8, 9, 12, 13, 14, 15, 16, 17, 18, 19},and may perform CSI-RS/CSI-IM measurements.

As another example, when the user equipment recognizes that DRS andPDSCH are multiplexed in SF of an unlicensed band cell, the userequipment may not distinguish between the CSI-RS configuration forCSI-RS/CSI-IM (i.e., CSI-RS/CSI-IM configuration) and the CSI-RS (DRS)configuration with respect to the corresponding SF. Also, the userequipment performs RRM measurements and/or CSI measurements byoverriding a CSI-RS configuration with the CSI-RS (DRS) configuration,that is, substituting the CSI-RS/CSI-IM configuration with the CSI-RS(DRS) configuration. Alternatively, the user equipment performs RRMmeasurements and/or CSI measurements by overriding the CSI-RSconfiguration with the CSI-RS/CSI-IM configuration, that is,substituting the CSI-RS (DRS) configuration with the CSI-RS/CSI-IMconfiguration. In the former case, the base station does not separatelyuse the CSI-RS REs for CSI-RS/CSI-IM, which needed to be transmitted tothe user equipment, and the user equipment measures the CSI-RS of theDRS to perform RRM measurements and/or CSI measurements without anyadditional RS overhead. In the latter case, the base station does notseparately use the CSI-RS REs (DRS), which needed to be transmitted tothe user equipment, and the user equipment measures the CSI-RS forCSI-RS/CSI-IM to perform RRM measurements and/or CSI measurementswithout any additional RS overhead.

As another example, when it is recognized by explicit signaling orimplicit signaling that DRS (CSI-RS) is transmitted in SF configured forCSI-RS/CSI-IM transmission in the unlicensed band cell, the userequipment may not distinguish between the CSI-RS/CSI-IM configurationand the CSI-RS (DRS) configuration with respect to the corresponding SF.Also the user equipment a) performs RRM measurements and/or CSImeasurements by overriding the CSI-RS/CSI-IM configuration with theCSI-RS (DRS) configuration, that is, substituting the CSI-RS/CSI-IMconfiguration with the CSI-RS (DRS) configuration or b) performs RRMmeasurements and/or CSI measurements by overriding the CSI-RS (DRS) withthe CSI-RS/CSI-IM configuration, that is, substituting the CSI-RS (DRS)configuration with the CSI-RS/CSI-IM configuration.

In the case of a), the base station may transmit the DRS including theCSI-RS without transmitting the CSI-RS REs for the CSI-RS/CSI-IM to theuser equipment. After receiving the DRS including the CSI-RS, the userequipment may measure the CSI-RS (DRS) to perform RRM measurementsand/or CSI measurements without additional RS overhead. Specifically, ifit is recognized by explicit signaling or implicit signaling that a DRS(CSI-RS) is transmitted in the SF configured for the CSI-RS/CSI-IMtransmission, the user equipment may assume that CSI-RS (CSI-RS/CSI-IM)is not transmitted in the corresponding SF and measure CSI-RS (DRS) toperform RRM measurements and/or CSI measurements.

In the case of b), the base station may transmit CSI-RS REs for theCSI-RS/CSI-IM to the user equipment and may not transmit CSI-RS (DRS).The user equipment may measure CSI-RS (CSI-RS/CSI-IM) to perform RRMmeasurements and/or CSI measurements without additional RS overhead.Specifically, if it is recognized by explicit signaling or implicitsignaling that a DRS (CSI-RS) is transmitted in the SF configured forthe CSI-RS/CSI-IM transmission, the user equipment may assume thatCSI-RS (DRS) is not transmitted in the corresponding SF and measureCSI-RS (CSI-RS/CSI-IM) to perform both RRM measurements and/or CSImeasurements.

Next, a description will be given of a solution of a case where atransmission resource (e.g., RE) of the CSI-RS (DRS) and a transmissionresource of the CSI-RS (CSI-RS/CSI-IM) collide with each other.

In Case 1), as shown in FIG. 21, when the DRS transmission is moved tothe SF other than the SF #0 and #5 due to the LBT, thePSS/SSS/CRS/CSI-RS that configures the DRS is transmitted in the OFDMsymbol index within the corresponding SF which is same as the OFDMsymbols index within the SF #0/#5, and the CSI-RS is transmitted in theOFDM symbol index #9/#10 according to the CSI-RS configuration. In sucha manner, when DRS is transmitted in SFs other than SF #0/#5 in additionto SF #0/#5, CSI measurements may be affected by a collision betweenCSI-RS (DRS) REs and CSI-RS REs for CSI-RS/CSI-IM measurements. In otherwords, in the SF where the DRS transmission is performed, if a collisionbetween CSI-RS (DRS) REs and CSI-RS/RS for CSI-RS/CSI-IM measurementshas occurred due to LBT, the CSI measurement is not performed or themeasurement performance deteriorates, so that there may be a problemwith the reliability of RRM measurement and CSI measurement. Therefore,an embodiment of in the present invention, even if the DRS transmissionis moved to the SF other than the SF #0/#5 due to the LBT, a method ofenabling RRM measurements for CSI-RS (DRS) and CSI measurements forCSI-RS/CSI-IM will be described and the method of ensuring measurementaccuracy and reliability will be described.

1. CSI-RS (DRS) and CSI-RS/CSI-IM may be configured to have differentresources (e.g., RE). Considering the case where the DRS is transmittedin the SF other than the SF (e.g., SF #0/#5) configured to betransmitted due to the LBT, CSI-RS (DRS) resources and CSI-RS/CSI-IMresources may be configured without overlapping. The base station maygenerate CSI-RS configuration information so that the CSI-RS (DRS)resource and the CSI-RS/CSI-IM resource do not overlap each other andnotify CSI-RS configuration information to the user equipment, and maytransmit CSI-RS (DRS) and CSI-RS/CSI-IM according to the CSI-RSconfiguration information to the user equipment. Accordingly, the userequipment may not expect CSI-RS (DRS) and CSI-RS/CSI-IM to betransmitted simultaneously in the same resource when detecting CSI-RS(DRS) and CSI-RS/CSI-IM. Also, the user equipment may detect CSI-RS(DRS) and CSI-RS/CSI-IM according to each CSI-RS configurationinformation. Under the assumption that resources for transmitting CSI-RS(DRS) and for transmitting CSI-RS/CSI-IM are different each other, theuser equipment may detect CSI-RS (DRS) and CSI-RS/CSI-IM according toeach CSI-RS configuration information.

2. Since CSI-RS (DRS) and CSI-RS/CSI-IM are configured independently,depending on the actual SF in which the DRS is transmitted, CSI-RS (DRS)and CSI-RS/CSI-IM may overlap in the same resource (e.g., RE) due toLBT. A method of detecting a CSI-RS (DRS) and a CSI-RS/CSI-IM when theCSI-RS (DRS) and the CSI-RS/CSI-IM collide with each other will bedescribed.

2-1) the CSI-RS (DRS) (Scrambling) sequence may be generated accordingto the SF index (slot index) or the SF number (slot number) where theCSI-RS (DRS) is transmitted. That is, whether the CSI-RS (DRS) istransmitted in the SF #O/#5 or the SF other than the SF #0/#5, theCSI-RS (DRS) sequence may depend on the SF index (slot index) or SFnumber (slot number) where the DRS is transmitted. Accordingly, when theCSI-RS (DRS) and the CSI-RS/CSI-IM overlap in the same resource(hereinafter referred to as collision resources) in SF, the base stationmay select one of CSI-RS (DRS) and CSI-RS/CSI-IM and transmit it. Thedetection of the CSI-RS (DRS) and the CSI-RS/CSI-IM is performed usingthe CSI-RS sequence generated based on the current SF index (slotindex). Therefore, regardless of which CSI-RS is transmitted in thecollision resource, the user equipment may detect the CSI-RS on thecollision resource using the CSI-RS sequence generated based on thecurrent SF index (slot index). That is, the user equipment may detectthe CSI-RS (DRS) or the CSI-RS/CSI-IM on the collision resource usingthe CSI-RS sequence generated based on the current SF index (slotindex).

On the other hand, the user equipment assumes that one of the CSI-RS(DRS) and CSI-RS/CSI-IM is dropped depending on whether to performdetection of CSI-RS (DRS) or detection of CSI-RS/CSI-IM in the collisionresource to perform a detection. That is, the user equipment performsRRM measurement and/or CSI measurement by performing detection of CSI-RS(DRS) and assumes that CSI-RS/CSI-IM is dropped. Conversely, the userequipment performs RRM measurement and/or CSI measurement by performingdetection of CSI-RS/CSI-IM and assumes that CSI-RS (DRS) is dropped. Inaddition, the CRS sequence based on the SF index used for the SSS (DRS)(e.g., SF #0/#5) or the CRS sequence based on the current SF index wherethe DRS is transmitted may be applied to the CRS (DRS).

2-2) the CSI-RS (DRS) sequence may not be generated according to the SFindex (slot index) or the SF number (slot number) where the DRS istransmitted. For example, the CSI-RS (DRS) sequence may depend on afixed SF index, depend on the SF index used for the SSS (DRS) (e.g., SF#0 and SF #5), or depend on the SF index used for CRS (DRS). The CRSsequence based on the SF index used for the SSS (DRS) (e.g., SF #0/#5)or the CRS sequence based on the current SF index where the DRS istransmitted may be applied to the CRS (DRS). For example, in a casewhere the CSI-RS (DRS) sequence depends on the SF index (slot index) ofthe SSS (DRS), when DRS is transmitted in SF #0 to SF #4, based on SF #0(slot #0/#1), a CSI-RS (DRS) sequence may be provided. On the otherhand, when DRS is transmitted in SF #5 to #9, a CSI-RS (DRS) sequencemay be provided based on SF #5 (slot #10/#11). Here, the fact that theCSI-RS sequence and the CRS sequence depend on the SF index (slot index)or are generated according to the SF index (slot index) may include thefact that the CSI-RS sequence and the CRS sequence are initialized basedon the corresponding SF index (slot index).

When the CSI-RS (DRS) and the CSI-RS/CSI-IM are configured to betransmitted from the same resource (e.g., RE)(hereinafter referred to ascollision resource) in the SF, the CSI-RS (DRS) sequence may not begenerated according to the SF index (slot index) or SF number (slotnumber) where the DRS is transmitted, and the CSI-RS sequence forCSI-RS/CSI-IM may be generated according to the current SF index (slotindex) or the current SF number (slot number). Accordingly, when CSI-RSs (e.g., CSI-RS (DRS) and CSI-RS/CSI-IM) having different purposes areconfigured to be transmitted in the same resource, the base stationtransmits only one of CSI-RSs.

As an example, in 3GPP TS 36.211 V12.6.0, the CRI-RS sequence isgenerated by Equation 2. The initialization value of the CSI-RS sequenceis given by Equation 3.

                                 [Equation  2]${{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {2m} )}}} )} + {j\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {{2m} + 1} )}}} )}}},{m = 0},1,\ldots \mspace{14mu},{N_{RB}^{\max,{DL}} - 1}$

Here, n_(s) represents a slot index in a radio frame, l represents anOFDM symbol index in the slot, c(●) represents a pseudo-random sequence,and N_(RB) ^(maxDL) represents the maximum number of RBs in the DL band.c(●) is initialized using the initialization value of Equation 3 at thebeginning of each OFDM symbol.

c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(CSI)+1)+2·N _(ID) ^(CSI)+N _(CP)   [Equation 3]

Here, n_(s) represents a slot index in a radio frame, and l representsan OFDM symbol index in a slot. N_(ID) ^(CS:) is configured by higherlayers (e.g., RRC), and is the same as N_(ID) ^(cell) if not configuredby higher layers. N_(ID) ^(cell) represents a physical cell ID. N_(CP)is a value representing a CP type, 1 for a normal CP and 0 for anextended CP. The slot index n_(s) in the radio frame has the followingrelationship with the SF index SF #.

TABLE 3 SF # 0 1 2 3 4 5 6 7 8 9 n_(s) 0 1 2 3 4 5 6 7 8 9 10 11 12 1314 15 16 17 18 19

Since the initialization value is determined based on each SF index inthe 3GPP Rel-12CSI-RS sequence, n_(s) in Equation 3 has a value of 0 to19 according to the SF where the CSI-RS is transmitted.

On the other hand, the CSI-RS (DRS) sequence is not generated accordingto the SF index (or slot index) where the DRS is transmitted. Forexample, when the sequence of the CSI-RS (DRS) depends on the SF index(e.g., SF #0 and SF #5) used for the SSS (DRS), n_(s) in Equation 3 hasonly a slot index corresponding to SF #0 or SF #5 according to the SFwhere the DRS is transmitted, as follows.

TABLE 4 SF # 0 1 2 3 4 5 6 7 8 9 n_(s) 0 1 0 1 0 1 0 1 0 1 10 11 10 1110 11 10 11 10 11

Therefore, when the CSI-RS is detected, the user equipment maydistinguish the CSI-RSs for different purposes by using the SF index(slot index) used for initializing the sequence of the CSI-RS. Forexample, it is assumed that the user equipment performs detectionprocess of the CSI-RS in SF #4. In this case, when the CSI-RS isdetected using the CSI-RS sequence initialized to the slot index #8 or#9, the user equipment determines the detected CSI-RS as CSI-RS(CSI-RS/CSI-IM). On the other hand, when the CSI-RS is not detectedusing the CSI-RS sequence initialized to the slot index #8 or #9 but isdetected using another sequence index (i.e., when the CSI-RS sequencedoes not depend on the SF index (slot index) of the current SF, or whenthe CSI-RS sequence is initialized using a value other than the SF index(slot index) of the current SF), the user equipment may determine thedetected CSI-RS as CSI-RS (DRS).

FIG. 24 illustrates a downlink receiving process according to anembodiment of the present invention.

Referring to FIG. 24, a user equipment may detect a CSI-RS in a timeunit #n on an unlicensed band cell (S2402). The time unit #n may besubframe #n or slot #n. Then, the user equipment may verify whether thedetected CSI-RS sequence is used only for the CSI measurement by usingthe initialization value of the CSI-RS sequence of the CSI-RS (S2404).Here, when the index of the time unit #n is used for the initializationvalue of the CSI-RS sequence, the detected CSI-RS sequence may be usedonly for CSI measurements. On the other hand, when the index of the timeunit #n is not used in the initialization value of the CSI-RS sequence,the CSI-RS sequence may be used for DRS. If the index of the time unit#n is not used in the initialization value of the CSI-RS sequence,predetermined value may be used instead of the index of the time unit#n. the predetermined value may be a specific SF index (or slot index),may be an SF index (or slot index) used for the SSS (DRS), may be an SFindex (or slot index) used for the CRS (DRS), or may be a slot indexn_(s) in Table 4. When CSI-RS is used for DRS, the CSI-RS may be usedfor CSI measurements and/or RRM measurements. More specifically, whenthe time unit #n is not the subframe #0 or #5 and the slot index of thesubframe #0 or #5 is used for the initialization value of the CSI-RSsequence, CSI-RS may be used for DRS.

The initialization value of the CSI-RS sequence may be given by thefollowing Equation:

c _(init)=2¹⁰·(7·(n ₂+1)+l+1)·(2·N _(ID) ^(CSI)+1)+2·N _(ID) ^(CSI) +N_(CP)

Here, l represents the OFDM symbol index within the slot, N_(ID) ^(CSI)represents a value configured by higher layers or a physical cellidentifier, N_(CP) has 0 or 1 depending on the CP (Cyclic Prefix) type,and n_(s) may have an index of the time unit #n according to the use ofthe CSI-RS, or has predetermined value. The predetermined value may be aspecific SF index (or slot index), may be an SF index (or slot index)used for the SSS (DRS), may be an SF index (or slot index) used for theCRS (DRS), or may be a slot index n_(s) in Table 4.

On the other hand, in the view point of the base station, DRStransmission for RRM measurement may be prioritized, so that CSI-RS(DRS) may be transmitted at the collision resource. In a case where acollision issue occurs, if there is explicit signaling or implicitsignaling for the presence of DRS (e.g., including blind detection ofDRS), the user equipment may assume that the CSI-RS (DRS) is transmittedat the collision resource. Accordingly, the user equipment may performRRM measurement and/or CSI measurement by performing detection of CSI-RS(DRS) according to the CSI-RS (DRS) sequence. Or, in a case where acollision issue occurs, if there is no explicit signaling or implicitsignaling for the presence of DRS (e.g., including blind detection ofDRS), the user equipment may perform CSI measurement by performingdetection of CSI-RS/CSI-IM according to the CSI sequence with respect tothe CSI-RS/CSI-IM configuration, that is, the CSI sequence depending oneach SF index.

Conversely, in the view point of the base station, since CSI-RStransmission for CSI-RS/CSI-IM measurement may be prioritized, CSI-RS(CSI-RS/CSI-IM) may be transmitted at the collision resource. In a casewhere a collision issue occurs on the same resource, if there isexplicit signaling or implicit signaling for the presence of DRS (e.g.,including blind detection of DRS), a user equipment receiving a CSI-RS(DRS) configuration and a CSI-RS/CSI-IM configuration from a basestation may assume that a CSI-RS (DRS) is transmitted at a collisionresource. Accordingly, the user equipment may perform RRM measurementand/or CSI measurement by performing detection of CSI-RS (DRS) accordingto the CSI-RS (DRS) sequence. Or, in a case where a collision issueoccurs, if there is no explicit signaling or implicit signaling for thepresence of DRS (e.g., including blind detection of DRS), the userequipment may perform CSI measurement by performing detection ofCSI-RS/CSI-IM according to the CSI sequence with respect to theCSI-RS/CSI-IM configuration, that is, the CSI sequence depending on eachSF index.

Meanwhile, the number of antenna ports of CSI-RS (DRS) and the number ofantenna ports of CSI-RS/CSI-IM may be different from each other. In thiscase, if CSI-RS configurations are set to be equal, REs mapped to CSI-RS(DRS) and CSI-RS/CSI-IM in time and frequency resources may overlap eachother. At this time, the base station may be configured to transmit aCSI-RS (DRS) with a small number of antenna ports at a collisionresource. In a case where a collision issue occurs on the same resource,if there is explicit signaling or implicit signaling for the presence ofDRS (e.g., including blind detection of DRS), since the number ofantenna ports for the CSI-RS (DRS) and the number of antenna ports forCSI-RS/CSI-IM may be known through the base station configuration, auser equipment receiving a CSI-RS (DRS) configuration and aCSI-RS/CSI-IM configuration from a base station may assume that a CSI-RS(DRS) is transmitted at a collision resource. Accordingly, the userequipment may perform RRM measurement and/or CSI measurement byperforming detection of CSI-RS (DRS) according to the CSI-RS (DRS)sequence.

The number of antenna ports of CSI-RS (DRS) and the number of antennaports of CSI-RS/CSI-IM may be different from each other. In this case,if CSI-RS configurations are set to be equal, REs mapped to CSI-RS (DRS)and CSI-RS/CSI-IM in time and frequency resources may overlap eachother. At this time, the base station may be configured to transmit theCSI-RS of the CSI-RS/CSI-IM with a larger number of antenna ports at acollision resource. In a case where a collision issue occurs on the sameresource, if there is explicit signaling or implicit signaling for thepresence of DRS (e.g., including blind detection of DRS), since thenumber of CSI-RS ports for transmitting DRS is different from the numberof CSI-RS ports that are periodic or aperiodic, a user equipmentreceiving a CSI-RS (DRS) configuration and a CSI-RS/CSI-IM configurationfrom a base station may assume that a CSI-RS (CSI-RS/CSI-IM) istransmitted at a collision resource. Accordingly, the user equipment mayperform RRM measurement and/or CSI measurement by performing detectionof CSI-RS (CSI-RS/CSI-IM) according to the CSI-RS (CSI-RS/CSI-IM)sequence.

Case 2) if CSI-RS configured for DRS is not configured in unlicensedband cell

When the CSI-RS configuration is not configured in the DRS, the OFDMsymbol index #9/#10 for the CSI-RS configured for the DRS is not used.Therefore, the CSI-RS configuration within the DMTC in the unlicensedband cell may be configured only as the CSI-RS configuration using theOFDM symbol #9/#10. In this case, in addition to the CSI-RS/CSI-IMmeasurement, the DRS function may be additionally obtained by detectingthe CSI-RS transmitted in the OFDM symbol index #9/#10. The CSI-RSconfigured for DRS and the CSI-RS/CSI-IM configured for CSI measurementare configured independently. Accordingly, in order to enableCSI-RS/CSI-IM measurements even when DRS transmissions are moved to SFsother than SF #0/#5 due to LBT, the base station may configure theCSI-RS/CSI-IM configuration and the CSI-RS (DRS) configurationidentically. Specifically, in the unlicensed band cell, the CSI-RSconfiguration, the MeasCSI-RS-Config which is the RRC parameter, may beset to one of resourceConfig {1, 2, 3, 6, 7, 8, 12, 13, 14, 15, 16, 17}except resourceConfig {0, 4, 5, 9, 10, 11, 18, 19} or one of a subset ofresourceConfig {1, 2, 3, 6, 7, 8, 12, 13, 14, 15, 16, 17}. A value ofthe CSI-RS configuration refers to Table 2. By configuring theCSI-RS/CSI-IM configuration as same as the CSI-RS (DRS) configuration,the collision of CSI-RS/CSI-IM and PSS/SSS (DRS) may be prevented andCSI measurement may be performed even when simultaneous transmission ofPDSCH and DRS is performed. Thus, when the user equipment is configuredto perform CSI-RS/CSI-IM measurements, the user equipment may assumethat resourceConfig {0, 4, 5, 9, 10, 11, 18, 19} is not used for theCSI-RS/CSI-IM measurements. Thus, the user equipment may performCSI-RS/CSI-IM measurements with the expectation that the CSI-RS/CSI-IMconfiguration may be set to one of resourceConfig {1, 2, 3, 6, 7, 8, 12,13, 14, 15, 16, 17} or one of a subset of resourceConfig {1, 2, 3, 6, 7,8, 12, 13, 14, 15, 16, 17}.

As another example, even if the DRS transmission is moved to SFs otherthan SF #0/#5 due to LBT, in order to enable CSI-RS/CSI-IM measurements,the CSI-RS configuration that may be allocated to the OFDM symbolindexes #5 and #6 to which the PSS/SSS (DRS) is allocated may beexcluded when configuring the CSI-RS for an unlicensed band cell. Thatis, the CSI-RS for the unlicensed band cell may be configured using onlythe CSI-RS configuration not allocated to the OFDM symbol indexes #5 and#6. Specifically, in the unlicensed band cell, the CSI-RS configurationmay be set to one of resourceConfig {1, 2, 3, 4, 6, 7, 8, 9, 12, 13, 14,15, 16, 17, 18, 19} except resourceConfig{0, 5, 10, 11} or one of asubset of resourceConfig {1, 2, 3, 4, 6, 7, 8, 9, 12, 13, 14, 15, 16,17, 18, 19}. A value of the CSI-RS configuration refers to Table 2. Inthe case of DRS alone transmission, as shown in FIG. 21, the last twoOFDM symbols in one of an SF are used as the CCA interval for LBT of thenext transmission. However, if DRS and PDSCH are multiplexed in SFexcept SF #0/#5, the last two OFDM symbols may be used for PDSCHtransmission and CSI-RS RE. Therefore, by configuring the CSI-RSconfiguration excluding the CSI-RS configuration, which may collide withthe PSS/SSS (DRS), to an unlicensed band cell (e.g., LAASCell),CSI-RS/CSI-IM measurement may be performed even when DRS and PDSCH aremultiplexed. When the user equipment is configured to performCSI-RS/CSI-IM measurements, the user equipment may assume thatresourceConfig {0, 5, 10, 11} is not used for the CSI-RS/CSI-IMmeasurements. Thus, the user equipment may expect that the CSI-RS/CSI-IMconfiguration is set to one of resourceConfig {1, 2, 3, 4, 6, 7, 8, 9,12, 13, 14, 15, 16, 17, 18, 19} or one of a subset of resourceConfig {1,2, 3, 4, 6, 7, 8, 9, 12, 13, 14, 15, 16, 17, 18, 19}, and may performCSI-RS/CSI-IM measurements.

FIG. 25 illustrates a configuration of a user equipment and a basestation according to an embodiment of the present invention. Theembodiment of the present invention, the user equipment may beimplemented by various types of wireless communication devices orcomputing devices that are guaranteed to be portable and mobility. Theuser equipment may be refered to as a station (STA), an MobileSubscriber (MS), or the like. In the embodiment of present invention,the base station may control and manage a cell (eg, macrocell,femtocell, picosell, etc.) corresponding to a service area and performfunction such as transmitting signal, designating channel, monitoringchannel, self-diagnosis, relay. The base station may be referred to asan evolved NodeB(eNB), an access point (AP), or the like.

Referring to FIG. 25, the user equipment 100 may include a processor110, a communication module 120, a memory 130, a user interface unit140, and a display unit 150.

The processor 110 may execute various commands or programs according toan embodiment of the present invention and process data in the userequipment 100. Further, the processor 100 may control all operations ofthe respective units of the user equipment 100 and control datatransmission/reception among the units. For example, the processor 110may receive/process the downlink signal according to the proposal of thepresent invention. (See FIGS. 1 to 24.)

The communication module 120 may be an integrated module that performsmobile communication using a mobile communication network and wirelessLAN access using a wireless LAN. To this end, the communication module120 may include a plurality of network interface cards such as cellularcommunication interface cards 121 and 122 and a wireless LAN interfacecard 123 in an internal or external type. In the figure, thecommunication module 120 is illustrated as the integrated module, butthe respective network interface cards may be independently disposedaccording to a circuit configuration or a purpose unlike the figure.

The cellular communication interface card 121 transmits/receives a radiosignal to/from at least one of a base station 200, an external device,and a server by using the mobile communication network and provides acellular communication service at a first frequency band based on acommand of the processor 110. The cellular communication interface card121 may include at least one NIC module using an LTE-licensed frequencyband. The cellular communication interface card 122 transmits/receivesthe radio signal to/from at least one of the base station 200, theexternal device, and the server by using the mobile communicationnetwork and provides the cellular communication service at a secondfrequency band based on the command of the processor 110. The cellularcommunication interface card 122 may include at least one NIC moduleusing an LTE-unlicensed frequency band. For example, the LTE-unlicensedfrequency band may be a band of 2.4 GHz or 5 GHz.

The wireless LAN interface card 123 transmits/receives the radio signalto/from at least one of the base station 200, the external device, andthe server through wireless LAN access and provides a wireless LANservice at the second frequency band based on the command of theprocessor 110. The wireless LAN interface card 123 may include at leastone NIC module using a wireless LAN frequency band. For example, thewireless LAN frequency band may be an unlicensed radio band such as theband of 2.4 GHz or 5 GHz.

The memory 130 stores a control program used in the user equipment 100and various resulting data. The control program may include a programrequired for the user equipment 100 to perform wireless communicationwith at least one of the base station 200, the external device, and theserver. The user interface 140 includes various types of input/outputmeans provided in the user equipment 100. The display unit 150 outputsvarious images on a display screen.

Further, the base station 200 according to the exemplary embodiment ofthe present invention may include a processor 210, a communicationmodule 220, and a memory 230.

The processor 210 may execute various commands or programs according tothe present invention and process data in the base station 200. Further,the processor 210 may control all operations of the respective units ofthe base station 200 and control data transmission/reception among theunits. For example, the processor 210 may transmit/process the downlinktransmission signal according to the proposal of the present invention.(See FIGS. 1 to 24.)

The communication module 220 may be an integrated module that performsthe mobile communication using the mobile communication network and thewireless LAN access using the wireless LAN like the communication module120 of the user equipment 100. To this end, the communication module 120may include a plurality of network interface cards such as cellularcommunication interface cards 221 and 222 and a wireless LAN interfacecard 223 in the internal or external type. In the figure, thecommunication module 220 is illustrated as the integrated module, butthe respective network interface cards may be independently disposedaccording to the circuit configuration or the purpose unlike the figure.

The cellular communication interface card 221 transmits/receives theradio signal to/from at least one of the user equipment 100, theexternal device, and the server by using the mobile communicationnetwork and provides the cellular communication service at the firstfrequency band based on a command of the processor 210. The cellularcommunication interface card 221 may include at least one NIC moduleusing the LTE-licensed frequency band. The cellular communicationinterface card 222 transmits/receives the radio signal to/from at leastone of the user equipment 100, the external device, and the server byusing the mobile communication network and provides the cellularcommunication service at the second frequency band based on the commandof the processor 210. The cellular communication interface card 222 mayinclude at least one NIC module using the LTE-unlicensed frequency band.The LTE-unlicensed frequency band may be the band of 2.4 GHz or 5 GHz.

The wireless LAN interface card 223 transmits/receives the radio signalto/from at least one of the user equipment 100, the external device, andthe server through the wireless LAN access and provides the wireless LANservice at the second frequency band based on the command of theprocessor 210. The wireless LAN interface card 223 may include at leastone NIC module using the wireless LAN frequency band. For example, thewireless LAN frequency band may be the unlicensed radio band such as theband of 2.4 GHz or 5 GHz.

In the figure, blocks of the user equipment and the base stationlogically divide and illustrate elements of the device. The elements ofthe device may be mounted as one chip or a plurality of chips accordingto design of the device. Further, some components of the user equipment100, that is to say, the user interface 140 and the display unit 150 maybe selectively provided in the user equipment 100. Further, somecomponents of the base station 200, that is to say, the wireless LANinterface 223, and the like may be selectively provided in the basestation 200. The user interface 140 and the display unit 150 may beadditionally provided in the base station 200 as necessary.

The method and the system of the present invention are described inassociation with the specific embodiments, but some or all of thecomponents and operations of the present invention may be implemented byusing a computer system having a universal hardware architecture.

The description of the present invention is used for illustration andthose skilled in the art will understand that the present invention canbe easily modified to other detailed forms without changing thetechnical spirit or an essential feature thereof. Therefore, theaforementioned exemplary embodiments are all illustrative in all aspectsand are not limited. For example, each component described as a singletype may be implemented to be distributed and similarly, componentsdescribed to be distributed may also be implemented in a combined form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to various communication devicesused in a wireless communication system (e.g., a station using anunlicensed band communication, an access point, or a station using acellular communication, a base station, etc.).

1-20. (canceled)
 21. A user equipment used in a cellular wirelesscommunication system, the user equipment comprising: a wirelesscommunication module; and a processor, wherein the processor isconfigured to: receive, from a base station, Channel StateInformation-Reference Signal (CSI-RS) configuration informationindicating one of plurality of CSI-RS configuration information includedin a CSI-RS configuration information set for a downlink cell, andreceive, from the base station, CSI-RS in a slot of the downlink cellaccording to the CSI-RS configuration information, wherein the CSI-RS istransmitted using at least one of antenna ports 15 to 22, wherein theCSI-RS configuration information set is a first CSI-RS configurationinformation set or a second CSI-RS configuration information set basedon whether the downlink cell operates in an unlicensed band, wherein thesecond CSI-RS configuration information set is part of the first CSI-RSconfiguration set, wherein when an index of the slot is not #0, #1, #10,or #11: when the CSI-RS is not used for Discovery RS (DRS), aninitialization value of a sequence of the CSI-RS is determined based ona first value, wherein the first value is equal to the index of theslot, and when the CSI-RS is used for DRS, the initialization value ofthe sequence of the CSI-RS is determined based on a second value,wherein the second value is not equal to the index of the slot.
 22. Theuser equipment of claim 21, wherein when the downlink cell operates in alicensed band, the first CSI-RS configuration information set includingone or more first CSI-RS configuration information related to OrthogonalFrequency Division Multiplexing (OFDM) symbols #5/#6, one or more secondCSI-RS configuration information related to OFDM symbols #9/#10, and oneor more third CSI-RS configuration information related to OFDM symbols#12/#13, wherein when the downlink cell operates in an unlicensed band,the second CSI-RS configuration information set, wherein the secondCSI-RS configuration information set does not comprise the one or morethird CSI-RS configuration information.
 23. The user equipment of claim22, wherein the second CSI-RS configuration information set does notcomprise the one or more first CSI-RS configuration information.
 24. Theuser equipment of claim 22, wherein the first CSI-RS configurationinformation set is a CSI-RS configuration {0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19} and the second CSI-RSconfiguration information set is a CSI-RS configuration {1, 2, 3, 6, 7,8, 12, 13, 14, 15, 16, 17}.
 25. The user equipment of claim 24, whereinthe OFDM symbols for CSI-RS according to a CSI-RS configurationinformation is given by the following Table. Number of CSI referencesignals configured 1 or 2 4 8 CSI-RS OFDM symbol OFDM symbol OFDM symbolconfiguration index index index 0 5, 6 5, 6 5, 6 1  9, 10  9, 10  9, 102  9, 10  9, 10  9, 10 3  9, 10  9, 10  9, 10 4 12, 13 12, 13 12, 13 55, 6 5, 6 6  9, 10  9, 10 7  9, 10  9, 10 8  9, 10  9, 10 9 12, 13 12,13 10 5, 6 11 5, 6 12  9, 10 13  9, 10 14  9, 10 15  9, 10 16  9, 10 17 9, 10 18 12, 13 19 12, 13


26. The user equipment of claim 21, wherein when the downlink celloperates in the unlicensed band and the CSI-RS is configured to DRS, theprocessor is further configured to perform a Radio Resource Management(RRM) measurement using the CSI-RS.
 27. The user equipment of claim 21,wherein the initialization value of the sequence of the CSI-RS is givenby the following Equation.c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(CSI)+1)+2·N _(ID) ^(CSI)+N _(CP) Here, l represents the OFDM symbol within a slot, N_(ID) ^(CSI)represents a value configured by higher layers or a physical cellidentifier, N_(CP) has 0 or 1 depending on a Cyclic Prefix (CP) type,and n_(s) has the first value or the second value.
 28. The userequipment of claim 21, wherein when the CSI-RS is transmitted using asingle of an antenna, a port of the single of the antenna is 15, whereinwhen the CSI-RS is transmitted using 2 antennas, ports of the 2 antennasare 15 to
 16. wherein when the CSI-RS is transmitted using 4 antennas,ports of the 4 antennas are 15 to 18, wherein when the CSI-RS istransmitted using 8 antennas, ports of the 8 antennas are 15 to
 22. 29.The user equipment of claim 21, wherein the CSI-RS sequence is given bythe following Equation.${{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {2m} )}}} )} + {j\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {{2m} + 1} )}}} )}}},{m = 0},1,\ldots \mspace{14mu},{N_{RB}^{\max,{DL}} - 1}$Here, N̂max,DL_RB is maximum number of RB in downlink and c(i) ispseudo-random sequence.
 30. The user equipment of claim 21, wherein whenthe CSI-RS is used for DRS, a period of transmission of the DRS is 40 msor 80 ms or 160 ms.
 31. A base station used in a cellular wirelesscommunication system, the base station comprising: a wirelesscommunication module; and a processor, wherein the processor isconfigured to: transmit, to a user equipment, Channel StateInformation-Reference Signal (CSI-RS) configuration informationindicating one of plurality of CSI-RS configuration information includedin a CSI-RS configuration information set for a downlink cell, andtransmit, to the user equipment, CSI-RS in a slot of the downlink cellaccording to the CSI-RS configuration information, wherein the CSI-RS istransmitted using at least one of antenna ports 15 to 22, wherein theCSI-RS configuration information set is a first CSI-RS configurationinformation set or a second CSI-RS configuration information set basedon whether the downlink cell operates in an unlicensed band, wherein thesecond CSI-RS configuration information set is part of the first CSI-RSconfiguration set, wherein when an index of the slot is not #0, #1, #10,or #11: when the CSI-RS is not used for Discovery RS (DRS), aninitialization value of a sequence of the CSI-RS is determined based ona first value, wherein the first value is equal to the index of theslot, and when the CSI-RS is used for DRS, the initialization value ofthe sequence of the CSI-RS is determined based on a second value,wherein the second value is not equal to the index of the slot.
 32. Thebase station of claim 31, wherein when the downlink cell operates in alicensed band, the first CSI-RS configuration information set includingone or more first CSI-RS configuration information related to OrthogonalFrequency Division Multiplexing (OFDM) symbols #5/#6, one or more secondCSI-RS configuration information related to OFDM symbols #9/#10, and oneor more third CSI-RS configuration information related to OFDM symbols#12/#13, wherein when the downlink cell operates in an unlicensed band,the second CSI-RS configuration information set, wherein the secondCSI-RS configuration information set does not comprise the one or morethird CSI-RS configuration information.
 33. The base station of claim32, wherein the second CSI-RS configuration information set does notcomprise the one or more first CSI-RS configuration information.
 34. Thebase station of claim 32, wherein the first CSI-RS configurationinformation set is a CSI-RS configuration {0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19} and the second CSI-RSconfiguration information set is a CSI-RS configuration {1, 2, 3, 6, 7,8, 12, 13, 14, 15, 16, 17}.
 35. The base station of claim 24, whereinthe OFDM symbols for CSI-RS according to a CSI-RS configurationinformation is given by the following Table. Number of CSI referencesignals configured 1 or 2 4 8 CSI-RS OFDM symbol OFDM symbol OFDM symbolconfiguration index index index 0 5, 6 5, 6 5, 6 1  9, 10  9, 10  9, 102  9, 10  9, 10  9, 10 3  9, 10  9, 10  9, 10 4 12, 13 12, 13 12, 13 55, 6 5, 6 6  9, 10  9, 10 7  9, 10  9, 10 8  9, 10  9, 10 9 12, 13 12,13 10 5, 6 11 5, 6 12  9, 10 13  9, 10 14  9, 10 15  9, 10 16  9, 10 17 9, 10 18 12, 13 19 12, 13


36. The base station of claim 31, wherein when the downlink celloperates in the unlicensed band and the CSI-RS is configured to DRS, theprocessor is further configured to perform a Radio Resource Management(RRM) measurement using the CSI-RS.
 37. The base station of claim 31,wherein the initialization value of the sequence of the CSI-RS is givenby the following Equation.c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(CSI)+1)+2·N _(ID) ^(CDI)+N _(CP) Here, l represents the OFDM symbol within a slot, N_(ID) ^(CSI)represents a value configured by higher layers or a physical cellidentifier, N_(CP) has 0 or 1 depending on a Cyclic Prefix (CP) type,and n_(s) has the first value or the second value.
 38. The userequipment of claim 31, wherein when the CSI-RS is transmitted using asingle of an antenna, a port of the single of the antenna is 15, whereinwhen the CSI-RS is transmitted using 2 antennas, ports of the 2 antennasare 15 to
 16. wherein when the CSI-RS is transmitted using 4 antennas,ports of the 4 antennas are 15 to 18, wherein when the CSI-RS istransmitted using 8 antennas, ports of the 8 antennas are 15 to
 22. 39.The user equipment of claim 31, wherein the CSI-RS sequence is given bythe following Equation.${{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {2m} )}}} )} + {j\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {{2m} + 1} )}}} )}}},{m = 0},1,\ldots \mspace{14mu},{N_{RB}^{\max,{DL}} - 1}$Here, N̂max,DL_RB is maximum number of RB in downlink and c(i) ispseudo-random sequence.
 40. The user equipment of claim 31, wherein whenthe CSI-RS is used for DRS, a period of transmission of the DRS is 40 msor 80 ms or 160 ms.